UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Comparative developmental studies of the floret and embryo sac in five species of Oryzopsis (Gramineae) Kam, Yew Kiew 1973

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1973_A1 K34.pdf [ 8.3MB ]
Metadata
JSON: 831-1.0101004.json
JSON-LD: 831-1.0101004-ld.json
RDF/XML (Pretty): 831-1.0101004-rdf.xml
RDF/JSON: 831-1.0101004-rdf.json
Turtle: 831-1.0101004-turtle.txt
N-Triples: 831-1.0101004-rdf-ntriples.txt
Original Record: 831-1.0101004-source.json
Full Text
831-1.0101004-fulltext.txt
Citation
831-1.0101004.ris

Full Text

nm  j  COMPARATIVE DEVELOPMENTAL STUDIES OF THE FLORET AND  EMBRYO SAC IN FIVE SPECIES OF ORYZOPSIS (GRAMINEAE)  by RAM YEE KIEW  B.Sc.  (Hons.)«» University of Malaya, Malaysia, 1967  M.Sc, University of Malaya, Malaysia, 1969  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF  THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY Iii the Department of BOTANY We accept this thesis as conforming to the required  standard  THE UNIVERSITY OF BRITISH COLUMBIA May, 1973  In presenting  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive  copying of t h i s t h e s i s  f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representatives.  I t i s understood that copying or p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission.  Department of  Botany  The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada  Date  July 5. 1973  ii  ABSTRACT Development of the floret and embryo sac of Oryzopsis virescens and 0. hymenoides was studied. Evidence from this study and from other studies on grass floret and embryo sac development has brought the following interpretations.  Histogenesis of the lemma, palea,  posterior lodicule and the gynoecial wall is similar, and indicates their foliar nature.  They are determinate organs, have a shallow site  of i n i t i a t i o n , and exhibit marginal growth. The anterior lodicules differ from them in having a deeper initiation s i t e .  The interpretation  of the anterior and posterior lodicules as reduced perianth structures of one whorl rather than as structures 'de novo' is preferred.  The  callus is formed by the downward projection of the base of the lemma. Developmentally, the stamens are stem-like.  The gynoecium consists  of a unit ascidiform gynoecial wall surrounding a terminal ovule. There are two styles, each of which develops from the lateral portions of the gynoecial wall. The floret apex is not used up in the formation of the gynoecial wall. The residual floret apex develops into the ovule.  The grass gynoecium may be considered  acarpellate. The ovule  is hemianatropous, bitegmic and pseudocrassinucellate. The micropyle is delimited by the inner integument. Embryo sac development is of the monosporic, 8-nucleate type.  The antipodals are proliferated.  The development of the floret and embryo sac of three other species of Oryzopsis was also studied. They are, namely, 0. micrantha, 0. k i n g i i , and 0. asperifolia.  Developmental features of a l l five  species of Oryzopsis were compared with developmental features of  iii  Oryzopsis miliacea, and of four species of Stipa, a c l o s e l y r e l a t e d genus.  These are, namely, S_. lemmoni, £5. hendersoni, S_.  and S_. r i c h a r d s o n i . Gaz.  107:  1-31)  tortilis  Cytotaxonomic studies by Johnson (1945.  i n the genus Oryzopsis  Bot.  indicate that 0. virescens  (n = 12) and 0. miliacea (n = 12) are members of the Old World section Piptatherum;  0. micrantha (n = 11), 0. k i n g i i (n = 11), and  a s p e r i f o l i a (n = 23), belong to the New  World section  0. hymenoides (n = 24) belongs to the New Intergradation of the genera Oryzopsis America i n the sections Oryzopsis  0.  Oryzopsis;  World section Eriocoma.  and S t i p a occurs i n North  and Eriocoma.  Qryzopsis  micrantha  resembles 0. miliacea i n c e r t a i n morphological features, while 0. k i n g i i i s a 'borderline' Oryzopsis-Stipa species.  Oryzopsis  hymenoides  i s known to hybridise with eleven species of Stipa. Thirty-one characters were abstracted from the developmental data and were analyzed  statistically.  The r e s u l t s indicate that 0.  virescens i s set apart from the f i v e other species of Oryzopsis the four species of S t i p a .  and  The a f f i n i t y of 0. hymenoides on the basis  of development i s with Stipa.  This further supports data from mor-  phology, d i s t r i b u t i o n and h y b r i d i z a t i o n studies and suggests that Oryzopsis hymenoides belongs to the genus Stipa. to be a discontinuous  There does not appear  v a r i a t i o n i n development between 0. miliacea,  0. micrantha, 0. a s p e r i f o l i a , 0. k i n g i i , £3. richardsoni, 0. hymenoides (Stipa) , 0. hendersoni, S_. lemmoni and S_. t o r t i l i s .  It would seem  that more comprehensive studies of the genus Oryzopsis w i l l either lead to i t s mergence with Stipa or at l e a s t to a r e d e f i n i t i o n of the sections of  Oryzopsis.  iv  TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  vi  LIST OF FIGURES  v i i  ACKNOWLEDGEMENTS  x  GENERAL INTRODUCTION  1  An evaluation of ontogenetic studies A b r i e f botanical history of Oryzopsis PART I  1 .  4 8  Introduction  8  Materials and methods  10  Observations  (a) . Oryzopsis virescens  12  (b). Oryzopsis hymenoides  27  Discussion.  36  Conclusion  54  PART I I  55  Introduction  55  Materials and methods.....  58  Observations  (a). Oryzopsis micrantha  59  (b) . Oryzopsis k i n g i i  65  (c) . Oryzopsis asperif o l i a  71  Discussion  77  Conclusion  89  LITERATURE CITED  90  APPENDIX FIGURES  vi  LIST OF TABLES Table I.  Page Reference table for comparison of stages in awn-lemma and callus development in Oryzopsis virescens and 0. hymenoides, using the stage of gynoecium development as a marker  II.  31  Reference table for comparison of stages i n awn-lemma and callus development in Oryzopsis virescens, 0. hymenoides, 0. micrantha, 0. kingii and 0. asperifolia, using the stage of gynoecium development as a marker...  III.  75  Comparison of developmental features of Oryzopsis virescens, 0. hymenoides, 0. micrantha, 0. kingii 0. asperifolia, 0. miliacea, Stipa lemmoni, S_. hendersoni, S_. t o r t i l i s and S_. richardsoni.  IV.  81  Similarity matrix ( % ) of Oryzopsis virescens, 0. hymenoides, 0. micrantha, 0. k i n g i i , 0. asperifolia, 0. miliacea, Stipa lemmoni, S. hendersoni, S. t o r t i l i s and S_. richardsoni  82  vii  LIST OF FIGURES Figure  -  1-6.  F l o r a l parts of Oryzopsis virescens and 0. hymenoides  7. 8 - 14.  Page  102  Diagramatic transverse section of grass f l o r e t  11  Stages i n f l o r e t development i n 0. virescens.  104  15 r, 20. Stages i n f l o r e t development i n 0. virescens  106  21 - 25.  Stages i n awn-lemma development i n 0. virescens  108  26 - 30.  Stages i n c a l l u s development i n 0. virescens  110  31 - 39.  Stages i n f l o r e t development i n 0. virescens  112  r  40 - 56. Stages i n stamen and anterior l o d i c u l e development i n 0. virescens.  114  57 - 72. Stages i n gynoecium development i n 0. virescens  116  73 - 77. Stages i n gynoecium development i n 0. virescens  118  78 - 84.  Stages i n ovule and embryo sac development i n 0. virescens  85 - 90.  91 - 98.  120  Stages i n ovule and embryo sac development i n 0. virescens  122  Stages i n embryo sac development i n 0. virescens  124  99 - 105. Stages i n f l o r e t development i n 0. hymenoides  126  106 - 112. Stages i n awn-lemma development i n 0. hymenoides  128  113 - 119. Stages i n callus development i n 0. hymenoides  130  120 - 128. Stages i n f l o r e t development i n 0. hymenoides  132  129 - 134. Stages i n f l o r e t development i n 0. hymenoides  134  viii  135 - 140. Ovule and early embryo sac development i n 0, hymenoides. 141 - 143. Stages in embryo sac development i n 0. hymenoides....  136 138  144 - 146. Fertilization and early post-fertilization stages i n 0. hymenoides  140  147 - 154. Floral parts of 0. micrantha, 0. k i n g i i and 0. asperifolia...  142  155 - 162. Stages i n floret development in 0. micrantha  144  163 - 167. Stages i n awn-lemma development i n 0. micrantha  146  168 - 173. Stages in callus development i n 0. micrantha  148  174 - 185. Stages in floret development in 0. micrantha  150  186 - 191. Ovule and embryo sac development i n 0. micrantha  152  192 - 196. Stages in embryo sac development i n 0. micrantha  154  197 - 204. Stages in floret development i n 0. kingii  156  205 - 211. Stages in awn-lemma development i n 0. kingii  158  212 - 218. Stages in callus development i n 0. k i n g i i .  160  219 - 231. Stages i n floret development in 0. kingii  162  232 - 239.  164  Ovule and embryo sac development in 0. k i n g i i .  240 - 244. Stages i n embryo sac development in 0. kingii  166  245 - 251. Stages i n floret development in 0. asperifolia.  168  252 - 257. Stages i n awn-lemma development in 0. asperifolia....  170  258 - 265. Stages in callus development i n 0. asperifolia.......  172  266 - 279. Stages i n floret development i n 0. asperifolia.......  174  280 - 284. Ovule and early embryo sac development i n 0. asperifolia  176  ix  285 - 288. Stages i n embryo sac development and f e r t i l i z a t i o n i n 0. asperifolia 289.  178  Inter-relationships of 0. virescens, 0. hymenoides, J2« micrantha. 0. k i n g i i , 0. asperifolia, 0. miliacea, Stipa lemmoni, S_. hendersoni, S_. t o r t i l i s and £>. richardsoni  85  290. Scanning electronmicrograph of young florets of 0. virescens  180  291. Scanning electronmicrograph of young florets of 0. virescens  180  292. Scanning electronmicrograph of young florets of 0. virescens 293. Sagittal section of floret of 0. virescens  182 184  294. Transverse section of top of ovary in 0. hymenoides.. 186 295.  Frontal longitudinal section of ovary of 0. hymenoides.  186  ACKNOWLEDGEMENTS  This research was carried out during the tenure of a Canadian Commonwealth Scholarship at The University of British Columbia for the years 1970-1973. It is with pleasure that the author expresses her appreciation to Dr. Jack Maze for guidance and counsel during the course of this work, and the use of his library.  1  GENERAL INTRODUCTION  This thesis consists essentially of two parts.  Part I is an  ontogenetic study of the floret and embryo sac of Oryzopsis virescens and 0. hymenoides, as such data would lead to a better understanding  of  the floret of Oryzopsis in particular, and of the Gramineae in general. Part II is an attempt to elucidate the relationships of 0. virescens, 0. hymenoides, 0. micrantha, 0. kingii and 0. asperifolia on the basis of data from developmental studies of the floret and embryo sac.  It is  hoped that developmental data can be used effectively as an adjunct to other characteristics in working out taxonomic problems.  An evaluation of ontogenetic studies It is generally accepted by most taxonomists that taxa are properly established on the basis of multiple correlations of characters  (Cronquist,  1968). Davis and Heywood (1965) , stressed that a l l stages of development of the plant should be examined for possible characters.  Yet ontogenetic  features have not received much attention from taxonomists-  Embryologi-  cal studies have been employed, successfully, to solve certain taxonomic problems (Maheshwari, 1950, 1961). Recent work by Mehlenbacher (1970), and Maze and co-workers (1971) , has shown that comparative studies on floret development in Oryzopsis and Stipa are useful in understanding the relationships of these two genera. A few reasons could be offered for this lack of popularity of applied ontogenetic studies. Results from ontogenetic investigations have a history of not bearing out the popular existing dogma of the time.  This  2  i s e s p e c i a l l y true i n the i n t e r p r e t a t i o n of the flower. research was  This branch of  set on a controversial course with the pronouncements of  Schleiden i n 1839 and Payer i n 1857  (both c i t e d by Mbelir5.no, 1970), that  ovules were not borne on carpels but were axis-borne.  This was of course  contrary to the prevalent carpel theory of that time.  The fact that  Schleiden was  l a t e r shown to be wrong i n h i s i n t e r p r e t a t i o n of f e r t i l i z a -  t i o n did not help to foster f a i t h i n the ontogenetic method.  Nonetheless,  ontogenetic research has continued to be one of the chief l i n e s along which attempts are made to solve the problem of organisation of angiosperm reproductive structures.  Even with today's improved techniques, no agree-  ment has been reached regarding the i n t e r p r e t a t i o n of the stamens and the carpels.  The i n t e r p r e t a t i o n of the stamen on the basis of histogenetic  analysis has resulted i n diametrically opposed conclusions.  Satina and  Blakeslee (1943), Barnard (1957a, b.), and Sharman (1960b) concluded that the stamens they studied were cauline, while Kaussman (1941), McCoy (1940), Boke (1947, 1949), and Kaplan (1968) hold that t h e i r investigations point to a f o l i a r i n t e r p r e t a t i o n for stamens.  Likewise, i n the Cyperaceae the  ovules are phyllosporous according to Schultze-Motel (1959), and cauline according to Barnard (1957b).  In Datura stramonium, Satina and Blakeslee,  (1943) concluded that the ovules are axis-borne, but Verzar-Petri and Baranyai Szentpetery (1960) stated that the ovules are c a r p e l l a r y . I t would appear, therefore, that the ontogenetic method cannot be used with any measure of r e l i a b i l i t y i n studies on descriptive f l o r a l morphology, and much less so i n comparative studies. contention that such a view-point i s erroneous.  I t i s the writer's  The place of ontogeny i n  f l o r a l enquiry has been staunchly defended by Thompson (1937).  One of the  3  causes for a l l these contradictions i s that most workers have not analysed t h e i r r e s u l t s s t r i c t l y on the basis of the histogenetic data they have obtained.  An example i s seen i n Schultze-Motel s paper (1959). 1  diagrams (Abb.  In his  7, lOd, 12, 17, 18, 20) the ovules are formed d i r e c t l y  from a p i c a l c e l l s and are therefore terminal, but he interprets them to be phyllosporous.  He adheres to the concept of the 'Entwicklungsfeld  Karpells' of Goebel (or  1  scheitelbedeckendes F e l d  1  des  of Eckardt, 1957), as  shown by the following excerpts "Die Primordien der Karpelle treten a l s 'scheitelbedeckendes Feld' (Eckardt, 1957, (o i n Abb.  S. 76) auf.  Die Samenanlage  7) entwickelt s i c h aus diesem Feld, i s also phyllospor".  The  description of his r e s u l t s i s dictated by the use of c e r t a i n i n t e r p r e t i v e terms.  As long as terms are used i n such a way,  phyllosporous1958).  the discussion about  versus a x i s - borne ovules becomes a travesty  (Fagerlind,  Another example i s i l l u s t r a t e d by the studies of Roth (1959),  and Pankow (1959), on the Primula placenta.  Using the same method (micro-  technique) , they obtained almost i d e n t i c a l r e s u l t s , which were interpreted by them i n diametrically opposed d i r e c t i o n s .  Pankow, on the basis of  his histogenetic r e s u l t s , interpreted the placenta as a continuation of the f l o r a l apex.  of  Roth, however, by a series of 'reasoned* deductions  concluded that the placenta i s of carpellary t i s s u e . The value of developmental studies has been stated cogently by Maze and co-workers (1971, 1972).  However, one must guard against an over-  emphasis of the r e s u l t s obtained by developmental studies.  In t h i s  connection, i t i s well to bear i n mind the opinions of von Guttenberg (1960), and Rohweder (1963), on the s i g n i f i c a n c e and l i m i t a t i o n s of histogenetic methods.  4  A b r i e f botanical history of Oryzopsis The genus Oryzopsis was  established i n 1803 by Michaux, based on a  single New World species, Oryzopsis a s p e r i f o l i a .  The genus has a very  complicated taxonomic h i s t o r y , an excellent account of which was Johnson (1945a).  given by  Only a b r i e f resume of the taxonomic relationships i n  the genus i s given here. As presently understood,  the genus Oryzopsis consists of approximately  1 6 species, occurring i n the cool and temperate regions of both the eastern and western hemispheres.  The species are placed i n three main morphologi-  c a l groups, each a taxonomic section (Hackel, 1889; taxonomic arrangement i s given below: Section  Piptatherum  0. miliacea (L.) Benth. and Hook. 0. virescens (Trin.) Beck. 0. paradoxa (L.) Nutt. 0. coerulescens (Desf.) Hack. 0. holciformis (Biel.) Hack. 0. racemosa (J.E.Smith) Ricker Section Oryzopsis 0. micrantha  (Trin. and Rupr.) Thurb.  0. pungens (Torr. ) Hitchc. 0. canadensis  (Poir.) Torr.  0. exigua Thurb. 0. k i n g i i (Boland.) Beal 0. a s p e r i f o l i a Michx. 0. s w a l l e n i i Hitchcock and Spellenberg  Johnson, 1945a).  The  5  Section Eriocoma 0. hymenoides (Roem. and Schult.) RIcker 0. contracta (B.L.Johnson) Shechter  The Old World section, Piptatherum,  consists of 5 d i p l o i d species  (2n = 24) which range i n d i s t r i b u t i o n from southern Europe and Northern A f r i c a to A s i a t i c Russia.  The s i x t h member, 0. racemosa, i s a p o l y p l o i d  (2n = 46) occurring i n North America. Species of the New World section Oryzopsis are rather d i s t i n c t at the d i p l o i d l e v e l (2n = 22) from those of Piptatherum.  The two polyploids i n  the section are 0. a s p e r i f o l i a (2n «= 46) and 0. s w a l l e n i i (2n = 34). Eriocoma i s a New World section of two polyploids, 0. hymenoides (2n = 48) and 0. contracta (2n = 48).  The l a t t e r species i s purported to  represent a s t a b i l i z e d hybrid l i n e derived from an 0. hymenoides x 0. micrantha cross (Shechter and Johnson, 1968). The genus Oryzopsis i s extremely  difficult  to circumscribe.  Consider-  able uncertainty s t i l l exists i n delimiting Oryzopsis from S t i p a , a c l o s e l y a l l i e d genus which tends to merge with Oryzopsis through the section Oryzopsis.  Characters of the lemma, awn, and c a l l u s , are t r a d i t i o n a l l y  r e l i e d on to d i s t i n g u i s h Oryzopsis from S t i p a .  In Ory zopsis the 1emma  i s r e l a t i v e l y broad, short, and indurate, the c a l l u s blunt and the awn deciduous.  In S t i p a the lemma i s long and slender, less indurate, the  c a l l u s i s sharp-pointed and the awn i s p e r s i s t e n t . Also, i n most species of Oryzopsis the inflorescence i s an open panicle, while i n S t i p a the panicle i s contracted. unreliably.  Taken independently,  these characters are highly  Even when considered together they do not e f f e c t i v e l y  6  d i s t i n g u i s h between the two genera, for c e r t a i n species resemble Oryzopsis i n some features, and S t i p a i n others.  I t has been the tendency f o r  systematists to assign uncertaind cases to Oryzopsis.  A recent example  i s 0. s w a l l e n i i (Hitchcock and Spellenberg, 1968). Studies i n f l o r e t development and embryology i n the two genera have been undertaken by Maze et a l . are continuing.  i n recent years (1970, 1971, 1972) and  Their data have proved to be useful i n assessing r e l a t i o n -  ships of three species of S t i p a .  Mehlenbacher (1970), a f t e r a thorough  study of 0. hendersoni Vasey found that this species i s closer to S t i p a than to Oryzopsis, and subsequently  transferred i t to S t i p a (Spellenberg  and Mehlenbacher, 1971). The development of the f l o r e t and the embryo sac (up to f e r t i l i z a t i o n ) of 5 species of Oryzopsis was studied by the author.  The 5 species are,  namely, 0. virescens, 0. hymenoides, 0. micrantha, 0. k i n g i i and 0. asperifolia.  They were chosen for the following reasons:  0. virescens  has the vegetative and f l o r a l features t r a d i t i o n a l l y associated with Oryzopsis  ( f l a t broad leaves, open panicle, short deciduous awn, plump  lemma and blunt c a l l u s ) , and i s considered to be most representative of the genus.  Oryzopsis hymenoides i s of i n t e r e s t because of i t s resem-  blance to species of the section Piptatherum i n several features, and because i n nature i t forms hybrids with several species of S t i p a , as Johnson demonstrated i n a series of papers (1943, 1945b, 1960, 1962, 1963).  I t i s e a s i l y distinguished from the Old World species by i t s  pubescent lemma and sharp pointed c a l l u s .  Oryzopsis micrantha, 0. k i n g i i  and 0. a s p e r i f o l i a are members of the section Oryzopsis  —  a section  7  marked by s p e c i a l i z a t i o n i n characters which merge with the genus S t i p a . Oryzopsis micrantha possesses characters.  an admixture of Piptatherum  Its a f f i n i t y to the section Piptatherum  E l i a s (1942), who  placed i t i n that section.  and  Oryzopsis  i s recognized by  Oryzopsis k i n g i i can best  be described as a borderline Stipa-Oryzopsis species.  I t possesses  features which are associated r e g u l a r l y with S t i p a (narrow involute leaves, closed panicle, twisted awn,  narrow lemma and sharp c a l l u s ) .  ment to either genus i s l a r g e l y a r b i t r a r y .  Its assign-  Oryzopsis a s p e r i f o l i a , the  type species of the genus, seems to occupy a p o s i t i o n , morphologically speaking, between the two extreme ends of the section Oryzopsis, as expressed by 0. micrantha and 0. k i n g i i (see Johnson, 1945a). Morphological and c y t o l o g i c a l studies so f a r have not resulted i n a s a t i s f a c t o r y delineation of the genus Oryzopsis, or a taxonomic arrangement that r e f l e c t s the i n t r i c a t e r e l a t i o n s h i p s between species of Oryzopsis, and between Oryzopsis and S t i p a .  More comprehensive studies  of the genus Oryzopsis are needed, and towards that end the author chosen developmental studies.  has  A thorough study of f l o r e t development  and embryology of two species, 0. virescens and 0. hymenoides, i s attempted — zoid  1  0. virescens because i t approaches the t r a d i t i o n a l 'Oryzop-  d e s c r i p t i o n ; 0. hymenoides because of i t s a f f i n i t i e s with section  Piptatherum  and i t s h y b r i d i z a t i o n with species of S t i p a .  that such a study w i l l lead to a better understanding floret.  It i s hoped  of the Oryzopsis  A l o g i c a l extension of the above i n v e s t i g a t i o n i s to seek charac-  ters of a developmental nature for purposes of comparison. for the 5 species mentioned.  This i s done  8  PART I  Developmental studies of the f l o r e t and embryos sac of Oryzopsis virescens and 0. hymenoides.  INTRODUCTION In recent years knowledge of the grass f l o r e t has increased through contributions from histogenetic studies. studies  Published descriptions of such  are found i n the papers by Cannon (1900),  Barnard (1955, 1957a), bacher (1970),  Sharman (1960a, 1960b),  and Maze et a l .  Bonnett (1953, 1961),  Klaus (1966),  (1970, 1971, 1972).  Mehlen-  However, there i s  s t i l l no unanimous i n t e r p r e t a t i o n of the grass f l o r e t , which remains a controversial topic i n plant morphology.  The controversy centres mainly  on the nature of the l o d i c u l e s , the stamens and the gynoecium, that i s , whether they are of a phyllome or caulome nature. Because of the imprecision of morphological terminology, i t i s imperative that the author c l a r i f i e s her use of terminology, e s p e c i a l l y a the terms phyllome and caulome.  Used i n d e s c r i p t i v e sense, morphologiA  c a l terms such as l e a f , bud, e t c . , are merely words for s t r u c t u r a l entities.  In a comparative sense the same words s i g n i f y mutually exclu-  sive categories.  While I t i s not wrong to use the word ' l e a f  i n the  sense of a category, the word conjures i n most minds the p i c t u r e of a foliage leaf. phyllome —  An a l t e r n a t i v e term of a more generalized character —  i s preferred.  Likewise, the structure described as a 'bud*  i s a member of the category caulome.  Defined i n general terms, a  9  phyllome i s an abstract e n t i t y to which belong l a t e r a l appendages of determinate growth.  These l a t e r a l appendages are d o r s i v e n t r a l , exhibit  marginal growth and have a shallow s i t e of i n i t i a t i o n . caulome encompasses structures of an a x i a l nature.  The category  These are of indeter-  minate growth, usually r a d i a l i n shape, do not undergo marginal growth, and have a deeper s i t e of i n i t i a t i o n .  I t i s rather fortunate that the  vegetative structures of the grasses that have been studied developmenta l l y lend themselves e a s i l y to categorization. The preceding paragraph w i l l undoubtedly unleash a torrent of c r i t i c i s m at the author, i d e n t i f i e d by 'Croizatian' and ' S a t t l e r i a n ' tags.  S a t t l e r (1966) made a very eloquent and v a l i d plea for a more  precise approach to comparative morphology.  But h i s semi-quantitative  -not  homology concept does^lend i t s e l f r e a d i l y to a p p l i c a t i o n , as he himself admitted.  For lack of a d d i t i o n a l methods, the author has to use the  • t r a d i t i o n a l tools of the trade' —  the established vocabulary of  comparative morphology i s s t i l l the most useful for communication of ideas (at l e a s t at the present time). In this part of the t h e s i s , the author reports her studies on the f l o r a l histogenesis i n two species of Oryzopsis, 0. virescens and 0. hymenoides.  Her present observations on f l o r a l histogenesis w i l l be  applied to the i n t e r p r e t a t i o n of the Oryzopsis f l o r e t i n p a r t i c u l a r , and to a c r i t i c a l discussion of the Gramineae f l o r e t i n general.  1 0  MATERIALS AND METHODS The f l o r e t of 0. v i r e s c e n s i s s h o r t and plump, t h e awn i s s h o r t and d e c i d u o u s , and the c a l l u s i s b l u n t ( F i g s . 1, 2, 3 ) .  O r y z o p s i s hymenoides  i s a wide-ranging grass i n a r i d areas of western North America.  I n the  shape o f i t s f l o r e t and t h e deciduous n a t u r e o f i t s awn, i t approaches 0. v i r e s c e n s ( F i g s . 4 , 5 , 6 ) , b u t i t s sharp c a l l u s and i t s p i l o s e lemma a r e c h a r a c t e r s found i n S t i p a , a genus c l o s e l y a l l i e d w i t h O r y z o p s i s , (see J o h n s o n , 1945a f o r t h e i n t r i c a t e r e l a t i o n s h i p s w i t h i n O r y z o p s i s and between i t and S t i p a ) . M a t e r i a l s used i n t h i s s t u d y were c o l l e c t e d from p l a n t s growing i n the Botany Garden a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a .  P l a n t s of  0. v i r e s c e n s were grown from seed o b t a i n e d t h r o u g h the I n t e r n a t i o n a l Seed Exchange; p l a n t s o f 0. hymenoides were t r a n s p l a n t s o f p o p u l a t i o n s c o l l e c t e d i n Canal F l a t s , B r i t i s h  Columbia.  F l o r e t s , e n t i r e young i n f l o r e s c e n c e s , o r p o r t i o n s o f young i n f l o r e s c e n c e s were f i x e d i n a F o r m a l i n - A c e t i c A c i d - A l c o h o l m i x t u r e , u s i n g 507. e t h y l a l c o h o l ( J o h a n s e n , 1 9 4 0 ) . 2,methoxyethanol  They were d e h y d r a t e d i n a  - a b s o l u t e a l c o h o l - n-propanol - n-butanol s e r i e s  (Feder and O ' B r i e n , 1 9 6 8 ) , and embedded i n P a r a p l a s t . t h a n 1 mm.  were o r i e n t e d b e f o r e s e c t i o n i n g .  F l o r e t s longer  T h i s was done v e r y s i m p l y  by u s i n g a p a i r o f f i n e f o r c e p s and a s m a l l s p a t u l a .  These i n s t r u m e n t s  were h e a t e d and used t o m e l t the wax around the f l o r e t . o f a s t e r e o - m i c r o s c o p e t h e f l o r e t was  W i t h the a i d  then moved around and p o s i t i o n e d  f o r s e c t i o n i n g e i t h e r i n a f r o n t a l or s a g i t t a l l o n g i t u d i n a l p l a n e . S e c t i o n s were c u t a t 6 - 7 u and s t a i n e d i n a c o m b i n a t i o n of s a f r a n i n , t a n n i c a c i d , orange G and i r o n alum (Sharman, 1 9 4 3 ) .  Drawings were  11  traced from a projection head on a Zeiss Ultraphot II microscope. A l l drawings are of sagittal sections unless otherwise stated, with the front (= anterior) side of the floret to the reader's l e f t .  Information  from sections of florets i n early stages of development was supplemented by scanning electron micrographs. The terms anterior (= front) vs. posterior (= back), and abaxial vs. adaxial are used to describe the orientation of the various parts of the floret.  These are used with reference to two axes: the rachilla axis and  the floret axis.(Fig. 7).  In those spikelets with more than one floret,  the lemma is situated away from the r a c h i l l a , while the palea is next to the r a c h i l l a .  That side of the floret with the lemma is said to be the  anterior side; the palea side is correspondingly  the posterior side.  Adaxial and abaxial denote two opposing surfaces of the same lateral structure, with reference to the axis on which i t is borne (in this case the floret axis).  For example, the lemma has an adaxial surface  (adjacent to the floret axis), and an abaxial surface (away from the floret axis).  •  —.  anterior stamen anterior (= front) lodicule (anterior side of floret)  floret axis  (posterior side of floret)  palea  posterior (= back) lodicule  rachilla axis FIG. 7. Cross-section of grass floret (diagramatic).  12  OBSERVATIONS  Oryzopsis virescens  (Trin.) Beck.  General f l o r e t organogenesis The  f i r s t structure to be i n i t i a t e d on the f l o r e t apex Is the  awn-lemma (Figs. 8, 15).  This occurs a f t e r the i n i t i a t i o n and  growth of the f i r s t and second glumes. next (Figs. 9, 18).  early  The palea and the stamens appear  There are three stamens, one anterior and  two  l a t e r a l , and unless otherwise stated, the stamen featured i n the drawings is the anterior one.  The l o d i c u l e s , two anterior and one  follow c l o s e l y (Figs. 10, 19).  posterior,  The c a l l u s and the gynoecial wall then  I n i t i a t e , at approximately the same time (Figs. 11, 20). structure to develop i s the ovule ( F i g . 13).  The l a s t  The shape of the  floral  floret.at  the megaspore stage i n embryo sac development i s shown i n Figure  14.  Floret a p i c a l meristem The  f l o r e t a p i c a l meristem has a tunica-corpus organization.  tunica i s one-layered.  The  The outermost corpus c e l l s often seem to form  a d i s t i n c t layer beneath the tunica (Fig. 15).  The f l o r e t apex i s  dome-shaped and remains so throughout organ formation, though i t undergoes some displacement i n the course of f l o r e t development (cf. Figs. 18, 19, 20).  15,  Early i n f l o r e t development, the f l o r e t apex i s more or  less aligned with the f l o r e t axis (Fig. 15).  During early growth of  the  anterior stamen and anterior l o d i c u l e the f l o r e t apex becomes p o s t e r i o r l y directed (Figs. 10, 19), and continues to be so oriented during growth of the gynoecial wall (Figs. 12, 34).  early  After the completion of  13  I n i t i a t i o n o f t h e g y n o e c i a l w a l l , t h e f l o r e t apex c o n t i n u e s growth as the o v u l e , b u t i t g r a d u a l l y becomes r e - o r i e n t e d  t o a v e r t i c a l and t h e n t o  an a n t e r i o r l y - d i r e c t e d p o s i t i o n ( F i g s . 7 8 , 7 9 , 8 0 ) .  Awn-lemma F o l l o w i n g t h e t e r m i n o l o g y and r e a s o n i n g o f Maze e t a l . ( 1 9 7 1 ) , t h e awn and t h e lemma a r e c o n s i d e r e d t o g e t h e r i n e a r l y development, and a r e referred  t o c o l l e c t i v e l y as t h e awn-lemma.  Awn-lemma i n i t i a t i o n i s  r-  i n d i c a t e d by a p e r i c l i n a l d i v i s i o n i n t h e protoderm on t h e a n t e r i o r  side  o f t h e f l o r e t a p i c a l m e r i s t e m , j u s t below t h e apex ( F i g . 1 5 ) . The i n i t i a t i n g d i v i s i o n i s f o l l o w e d by f u r t h e r p e r i c l i n a l d i v i s i o n s i n t h e protoderm and ground m e r i s t e m , i n v o l v i n g t h r e e t o f o u r c e l l s i n t h e vertical direction.  The awn-lemma i s formed from c e l l s o f t h e p r o t o d e r m  and t h e f i r s t l a y e r o f t h e ground m e r i s t e m .  From t h e a n t e r i o r  side,  i n i t i a t i n g d i v i s i o n s s p r e a d around t h e l a t e r a l f l a n k s o f t h e f l o r e t apex. The l a t e r a l s p r e a d o f d i v i s i o n s r e s u l t s i n t h e f o r m a t i o n o f a  crescentic  p r o t u s i o n w h i c h i s h i g h e r on t h e a n t e r i o r s i d e and s l o p e s down p o s t e r i o r ly  ( F i g s . 16, 16a).  Upward growth o f t h e p r i m o r d i u m i s m a i n l y t h e r e s u l t  of s u b - a p i c a l a c t i v i t y  (Fig. 17).  I n c r e a s e d a p i c a l a c t i v i t y a t t h e p o i n t o f o r i g i n o f t h e awn-lemma primordium r e s u l t s i n a f r e e e x t e n s i o n ( F i g s . 1 8 , 290). e x t e n s i o n i s t h e young awn. anterior portion  F o r ease o f d i s c u s s i o n ,  This  anterior  growth o f t h e  o f t h e awn-lemma p r i m o r d i u m w i l l be c o n s i d e r e d  first,  and t h e l a t e r a l p o r t i o n s l a t e r . I n t h e young awn i n c r e a s e i n h e i g h t by a p i c a l a c t i v i t y i s soon f o l l o w e d by i n t e r c a l a r y g r o w t h .  Cellular d i f f e r e n t i a t i o n , using  cell  14  vacuolation as an i n d i c a t i o n , occurs very early i n awn development.  The  c e l l s at the d i s t a l end become vacuolated when the awn-lemma primordium i s ca. 150 u i n height.  Growth i n g i r t h of the awn i s the r e s u l t of c e l l  vacuolation and p e r i c l i n a l d i v i s i o n s i n the ground meristem ( F i g . 19). At this stage i t i s not possible to d i s t i n g u i s h the awn base from the lemma below i t .  The c e l l s i n the proximal one-third of the awn-lemma  primordium are smaller than those i n the d i s t a l two-thirds primordium, and are also vacuolate  to a lesser degree.  of the  Certain i n t e r e s t -  ing growth phenomena are observed at the time the gynoecial wall i n i t i a t e s . In the adaxial ground meristem  of the awn-lemma, at a point more or less  l e v e l with the i n i t i a t i n g gynoecial d i v i s i o n , oblique d i v i s i o n s are seen (Fig. 20). The adaxial ground meristem c e l l s i n t h i s region become a c t i v e l y m i t o t i c and form a group of small, densely cytoplasmic  cells  with no p a r t i c u l a r arrangement (Figs. 21, 22). At the same time the corresponding abaxial ground meristem c e l l s undergo p e r i c l i n a l and a n t i clinal divisions.  Figure 22 shows the awn-lemma junction when the  gynoecial wall appears on the posterior side of the f l o r a l apex.  Further  d i v i s i o n s i n the ground meristem on the adaxial side are mostly p e r i c l i n a l , forming regular c e l l f i l e s .  The lemma apex becomes s l i g h t l y  expanded ( F i g . 23). Adaxial protodermal c e l l s of the lemma apex also s t a r t to divide p e r i c l i n a l l y , while the abaxial protoderm remains onelayered.  Continued meristematic a c t i v i t y , together with re-oriented  planes of growth, greatly increases the thickness of the lemma apex (Fig. 24). C e l l enlargement and vacuolation of the c e l l f i l e s push each side of the apex outwards so that the f u l l y expanded lemma apex has a double convex shape, with the apex of each convexity  directed  15  upwards. This i s seen in Figure  25, at a stage when the integuments of  the ovule are formed. The abaxial protoderm has adjusted to the increase in bulk of the abaxial ground meristem by an increased number of antic l i n a l divisions.  On the adaxial side there is a multiple protoderm of  about two to four cells deep, spread over the upper one-third of the convexity.  Accomodation of the adaxial protodermal cells to the increased  volume of the ground meristem is through c e l l division and enlargement. The portion of the lemma that eventually encloses the palea and the rest of the floret develops from the lateral portions of the lemma (Fig. 292).  Growth of the lateral portions i s of course co-ordinated with  that of the rest of the lemma. The lateral portions of the lemma grow around to the posterior side of the floret but do not meet.  Initially  they are taller on the anterior side and barely cover the base of the floret (Fig. 291).  Concurrent with the growth of the anterior portion  of the lemma, the lateral portions grow upwards, elongate tremendously and overtop the rest of the floret.  Just prior to the formation of the  integument in.ovule development, the upper portions of the free margins of the lemma have increased in height more than that part of the lemma to which the awn is attached (Fig. 24).  This results in the free edges of  the lemma forming two lobes (or 'ears') i n front of the awn. Cell enlargement i n the lemma finally obscures the patterns of cell divisions that resulted in the characteristic shape of the lemma apex. Cells at the awn-lemma junction remain small, and eventually become heavily l i g n i f i e d , with abundant simple pits i n the c e l l walls. They do not form a cambium-like layer as that reported for Stipa lemmoni by Maze et a l . (1972).  1 6  Callus The c a l l u s i s i n i t i a t e d t h r o u g h c e l l enlargement and c e l l  division  i n t h e ground m e r i s t e m a t t h e base o f t h e lemma, on t h e a n t e r i o r of the f l o r e t  ( F i g . 26).  of the gynoecial w a l l .  side  T h i s o c c u r s a t about t h e time o f i n i t i a t i o n  At t h i s s t a g e t h e base o f the f l o r e t where i t  i s a t t a c h e d t o the r a c h i l l a i s a l m o s t h o r i z o n t a l . I n i t i a l growth s t a g e s o f t h e c a l l u s i n v o l v e p e r i c l i n a l d i v i s i o n s , vacuolation  and e x p a n s i o n , i n a d i r e c t i o n p a r a l l e l w i t h the a d j a c e n t  p r o t o d e r m o f t h e c e l l s o f t h e ground m e r i s t e m ( F i g . 2 7 ) .  The protoderm  c e l l s n e i t h e r d i v i d e p e r i c l i n a l l y nor enlarge p e r c e p t i b l y . anticlinally  They d i v i d e  t o keep pace w i t h the i n c r e a s e i n volume o f t h e groumd  meristem ( F i g s . 27, 2 8 ) .  By t h e t i m e t h e g y n o e c i a l w a l l i s f u l l y  i n i t i a t e d t h e c a l l u s has d e v e l o p e d i n t o a rounded hump w i t h a downwardd i r e c t e d apex ( F i g s . 2 7 , 2 8 ) . Concomitant w i t h t h e growth o f t h e c a l l u s , t h e f o r m e r l y h o r i z o n t a l floret-rachilla  j u n c t i o n s t a r t s t o t i l t i n an a n t i - c l o c k w i s e d i r e c t i o n .  The r a c h i l l a a l s o i n c r e a s e s i n w i d t h ( F i g s . 2 7 , 2 8 , 2 9 , 3 0 ) . o r i e n t a t i o n of the f l o r e t - r a c h i l l a the f o l l o w i n g growth phenomena.  Re-  j u n c t i o n can be a t t r i b u t e d i n p a r t t o  On t h e a n t e r i o r and p o s t e r i o r  sides  o f t h e r a c h i l l a , p e r i c l i n a l d i v i s i o n s i n t h e ground m e r i s t e m produce f i l e s o f c e l l s p e r p e n d i c u l a r to the protoderm ( F i g s . 27, 2 8 ) .  Anticlinal  d i v i s i o n s i n t h e ground m e r i s t e m on t h e p o s t e r i o r s i d e o f t h e r a c h i l l a form f i l e s o f c e l l s p a r a l l e l  w i t h t h e a d j a c e n t protoderm ( F i g . 2 9 ) .  Cell  enlargement i n t h e ground m e r i s t e m on t h e p o s t e r i o r s i d e o f t h e r a c h i l l a i n t h e a x i l o f t h e second glume ( F i g . 30) and p o s s i b l y c e l l  enlargement  i n t h e t i s s u e s below t h e second glume ( u n f i g u r e d ) l e a d t o growth upward  17  o f t h e p o s t e r i o r s i d e s o f t h e r a c h i l l a and t h e lemma b a s e . The  continued enlargement, p a r a l l e l w i t h  t h e p r o t o d e r m , o f t h e ground  meristem c e l l s i n the c a l l u s , together w i t h the elongation dermal c e l l s , pushes t h e c a l l u s f u r t h e r down ( F i g . 3 0 ) .  of the proto-  T h i s downward  growth i s c o n c o m i t a n t w i t h f u r t h e r t i l t i n g upwards o f t h e lemma base and the r a c h i l l a on t h e p o s t e r i o r s i d e , as d i s c u s s e d above ( F i g s . 2 9 , 3 0 ) . When f u l l y m a t u r e , t h e rounded t i p o f t h e c a l l u s i s o n , o r c l o s e t o , the v e r t i c a l a x i s o f t h e f l o r e t  (Fig. 14).  Palea The  p a l e a a r i s e s a f t e r e a r l y growth o f t h e awn-lemma p r i m o r d i u m  t h r o u g h t h e p e r i c l i n a l d i v i s i o n s o f s e v e r a l p r o t o d e r m a l c e l l s on t h e p o s t e r i o r s i d e o f t h e f l o r e t apex ( F i g s . 1 8 , 3 1 ) .  The i n i t i a t i n g  d i v i s i o n s s p r e a d around t h e f l a n k s o f t h e apex t o t h e a n t e r i o r but do n o t e n c i r c l e t h e a p e x .  Following  side,  i n i t i a t i o n , the c e l l s under-  l y i n g t h e p r o t o d e r m a l i n i t i a l s d i v i d e p e r i c l i n a l l y , b u t t h e major c o n t r i bution 33).  t o t h e p a l e a i s made by d e r i v a t i v e s o f t h e protoderm ( F i g s . 3 2 , Growth o f t h e p a l e a i s t h r o u g h a p i c a l and s u b a p i c a l  activity.  O b l i q u e - a n t i c l i n a l d i v i s i o n s o f the a p i c a l i n i t i a l s g i v e r i s e t o t h e palea protoderm, w h i l e meristmatic a c t i v i t y o f the subapical  cells  gives r i s e t o the i n t e r n a l tissues o f the palea ( F i g s . 34, 35). growth i s due t o m a r g i n a l and s u b m a r g i n a l i n i t i a l s . i n e a r l y s t a g e s i s m a i n l y due t o c e l l d i v i s i o n .  Marginal  Growth o f t h e p a l e a  A f t e r the gynoecial  w a l l i s c o m p l e t e l y i n i t i a t e d around t h e a p e x , t h e p a l e a grows m a i n l y through c e l l e l o n g a t i o n .  A t m a t u r i t y t h e p a l e a has a s h o r t b i s e r i a t e  a p i c a l p o r t i o n and a b r o a d base ( F i g s . 3 6 a , b , c ) .  The c e l l s w h i c h  18  enlarge the most are those on the a d a x i a l  Posterior  lodicule  The p o s t e r i o r l o d i c u l e (Figs. 291, 292) palea.  surface.  appears s h o r t l y a f t e r the  I t s i n i t i a t i o n i s i n d i c a t e d by p e r i c l i n a l d i v i s i o n s i n the proto-  derm on the p o s t e r i o r side of the f l o r e t a p i c a l meristem , j u s t above the palea (Figs. 20, 33). the f l o r e t a p i c a l meristem.  In other words, i t i n i t i a t e s d i r e c t l y from Protodermal d e r i v a t i v e s contribute  to the t i s s u e s of the p o s t e r i o r l o d i c u l e .  solely  E a r l y growth i s the r e s u l t  of a p i c a l and subapical a c t i v i t y (Figs. 34, 35), and r e s u l t s i n an organ which i s considerably thinner than the palea ( F i g . 37).  At maturity the  p o s t e r i o r l o d i c u l e i s a t h i n f l a p of homogenous, non-vascularised t i s s u e , about three to four c e l l s t h i c k (Figs. 38,  Anterior The  39).  lodicule i n c e p t i o n and development of the a n t e r i o r l o d i c u l e s i s d i f f e r e n t  from that of the p o s t e r i o r l o d i c u l e s .  I n i t i a t i o n of the  anterior  l o d i c u l e s i s through p e r i c l i n a l d i v i s i o n s i n the f i r s t l a y e r of the ground meristem, i n between the bases of the developing stamens. i n i t i a t i o n occurs over 2 - 3  The  s i t e of  c e l l s i n l o n g i t u d i n a l s e c t i o n (Figs. 19,  I t has a deeper s i t e of i n i t i a t i o n than the p o s t e r i o r l o d i c u l e .  40).  Follow-  i n g the i n i t i a t i n g d i v i s i o n s , the protoderm c e l l s d i v i d e p e r i c l i n a l l y (Figs. 34, 42).  In cross s e c t i o n , two separate s i t e s of i n i t i a t i o n of  the a n t e r i o r l o d i c u l e s are seen ( F i g . 45).  Through repeated p e r i c l i n a l  d i v i s i o n s i n the ground meristem short f i l e s of c e l l s are formed ( F i g . 41).  The a n t e r i o r l o d i c u l e s at t h i s stage appear as bulges ( F i g . 42).  19  Growth i n height of the a n t e r i o r l o d i c u l e s i s i n t e r c a l a r y (Figs. 43, 44).  A p i c a l growth i s not d i s t i n c t .  Each a n t e r i o r l o d i c u l e i s attached  to the f l o r e t a x i s by a very broad base ( F i g . 48).  The c e l l s of the  mature a n t e r i o r l o d i c u l e form a homogenous t i s s u e , supplied by two vascular strands ( F i g . 49). Marginal growth i s i n i t i a t e d when p e r i c l i n a l d i v i s i o n s i n the protoderm spread  from the s i t e of l o d i c u l e i n i t i a t i o n i n a p o s t e r i o r  d i r e c t i o n ( F i g . 46).  A d i s t i n c t p o s t e r i o r margin i s soon formed ( F i g .  47).  When t h i s i s d i s c e r n i b l e an a n t e r i o r margin s t a r t s to grow ( F i g .  47).  Growth i s maximum i n the a n t e r i o r p o r t i o n of the l o d i c u l e so that  t h i s p o r t i o n of the l o d i c u l e i s t h i c k e s t (Figs. 48, 49, 50).  Stamens Stamen i n i t i a t i o n s t a r t s w i t h p e r i c l i n a l d i v i s i o n s i n the f i r s t l a y e r of the ground meristem (Figs. 18, 51).  At i n i t i a t i o n and during  subsequent stages of development the protodermal c e l l s d i v i d e a n t i c l i n a l l y only.  E a r l y growth r e s u l t s from d i v i s i o n s i n the ground meristem (Figs.  19, 40).  The young stamen primordium very e a r l y assumes a globose  form ( F i g . 291). Anther formation involves almost a l l the c e l l s of the stamen primordium.  Only a few c e l l s at the basal p o r t i o n of the primordium undergo  extensive elongation to form the filament.  A young anther primordium  i n cross s e c t i o n soon becomes s l i g h t l y 4-lobed ( F i g . 52).  Several  hypodermal c e l l s become d i f f e r e n t i a t e d i n each lobe and are recognised by t h e i r l a r g e r s i z e and conspicuous n u c l e i ( F i g . 53).  These form  20  the archesporial c e l l s .  Stages i n anther development are shown i n  Figures 54, 55, and 292. layers.  The f u l l y developed anther has four wall  The innermost w a l l layer, or tapetum, i s of the secretory type.  Gynoecium  _^  The gynoecium i s the l a s t structure to develop from the f l o r e t a p i c a l meristem.  The gynoecial wall i s f i r s t indicated by one or two p e r i c l i n a l  divisions i n the protoderm on the anterior side of the f l o r e t primordium, between the adaxial furface of the anterior stamen and the apex of the primordium ( F i g . 57).  That i s , i t i n i t i a t e s as a l a t e r a l appendage.  This i s followed by s i m i l a r d i v i s i o n s i n the ground meristem underlying the protodermal i n i t i a l s . 58, 293).  A f o l d develops l a t e r a l l y on the apex (Figs.  Such m i t o t i c a c t i v i t i e s , s t a r t i n g on the anterior  side of  the f l o r e t apex, extend around both flanks of the apex (Figs. 59, 60, 61), and eventually appear on the posterior side (Figs. 62, 63).  The  gynoecial wall i s thus transformed from a crescent-shaped primordium to a ring-shaped one.  The posterior rim of the gynoecial wall becomes  the s i t e of active m i t o t i c d i v i s i o n s (Figs. 64, 65, 66).  The  gynoecial  wall then grows upward as a tube (Figs. 67, 68, 69, 70). The t o t a l f l o r a l apex i s not used up i n the formation of the gynoec i a l wall.  Following the i n i t i a t i o n of the ring-shaped primordium, the  apex of the f l o r e t primordium increases i n s i z e (Figs. 64, 65). develops d i r e c t l y  It  into the ovule.  The two l a t e r a l sides of the gynoecial wall develop i n t o s t y l e branches (Figs. 68, 71, 72).  The s t y l e branches are s o l i d and i n i t i a t e  stigmatic hairs through c e l l elongation i n the protoderm c e l l s ( F i g . 73),  2 1  at a time when the megaspore mother c e l l i s formed i n embryo sac ment.  develop-  These enlarged club-shaped c e l l s undergo a n t i c l i n a l and oblique  d i v i s i o n s to form stigmatic hairs (Fig. 74).  The stigmatic hairs are  mostly l o c a l i z e d on the inner surfaces of each s t y l e . Each s t y l e has two areas of s p e c i a l i z e d tissue, the stigmatoid and the vascular.  In Figure 74, the u n f i l l e d space i n the s t y l e , towards  the outer surface of the s t y l e , represents the vascular region, and the stigmatoid region, which i s not represented, i s situated towards the inner surface of the s t y l e , near the stigmatic h a i r s .  I l l u s t r a t i o n s of  the stigmatoid region are given i n the account on 0. hymenoides. be  The loculus of the ovary does not appear t o c l o s e d p r i o r to or A  during f e r t i l i z a t i o n ( F i g . 76).  Tissue p r o l i f e r a t e d on the inner surfaces  of the ovary wall bring the edges of the ovary wall closer together, but a c l e f t i s l e f t at the top of the ovary (Figs. 75, 75a, 76).  The c l o s i n g  tissue consists of a group of small c e l l s , and i s the 'stylar core' described by Arber (1934). The vasculature of the gynoecium was of f l o r e t s .  studied from s e r i a l sections  Figure 77 shows a series of transverse sections of a f l o r e t  at the megaspore stage.  Subsequent to the detachment of a trace to each  of the three stamens, the provascular tissue of the f l o r a l axis i s i n the form of a cylinder (Fig. 77a).  At a higher l e v e l , an anterior  gynoecial trace i s detached from this provascular cylinder ( F i g . 77b), and a l i t t l e higher than t h i s , two l a t e r a l traces become detached.  The  remainder of the central provascular axis continues d i r e c t l y to the ovule (Figs. 77c,d).  There are, as shown i n Figure 77d, four vascular  22  bundles i n the ovary:  two l a t e r a l , one anterior and one posterior.  of the l a t e r a l vascular bundles enters a s t y l e (Figs. 77e,f,g).  Each  The  posterior vascular bundle i s the l a r g e s t , and supplies the ovule.  Both  the anterior and posterior vascular bundles terminate i n the ovary wall (Figs. 82a, 83a).  Early ovule and embryo sac development Ovule The whole f l o r e t apex i s not consumed i n the formation of the gynoecial w a l l .  The r e s i d u a l apex forms a small convex dome, consisting  of dense meristematic c e l l s ( F i g . 78). ovule.  I t develops d i r e c t l y into the  With the formation of the ring-shaped gynoecial w a l l there i s  a s l i g h t s h i f t i n p o s i t i o n of the f l o r e t apex so that instead of i t s being directed towards the palea i t becomes a n t e r i o r l y directed ( F i g . 79).  Concomitant with the growth of the posterior side of the gynoecial  w a l l , the apex increases rapidly i n s i z e , and continues to t i l t l y ( F i g . 80).  anterior-  By the time the integuments are i n i t i a t e d , the ovule  appears to be borne l a t e r a l l y on the posterior side of the gynoecial wall ( F i g . 81).  As the ovule continues to grow, i t t i l t s towards the  lemma (Fig.82a), becoming orthotropous at the megaspore mother c e l l stage ( F i g . 83a), then bending downward (Figs. 85a, 88a, 90a), f i n a l l y becoming hemianatropous at the 8-nucleate stage i n embryo sac development ( F i g . 91a). Integuments Both the inner and outer integuments are of protodermal o r i g i n .  They  23  are i n i t i a t e d as r i n g meristerns.  The inner integument i n i t i a t e s f i r s t  and i s i n d i c a t e d by protodermal p e r i c l i n a l d i v i s i o n s on both the upper and lower sides of the nucellus ( F i g . 81). I n i t i a t i n g d i v i s i o n s of the outer integument are f i r s t seen on the upper s i d e ( F i g . 82), by which time the megaspore mother c e l l i s d i s t i n c t . The inner integument forms the micropyle.  In e a r l y stages of i t s  development the inner integument i s two c e l l s t h i c k . stage the micropyle i s formed. ment s t a r t to d i v i d e .  By the megaspore  C e l l s a t t h i s end of the inner integu-  The r e s u l t i s an inner integument w i t h a thickened  micropylar p o r t i o n while the r e s t of i t remains two c e l l s t h i c k (Figs.90, 91).  This t h i c k e r p o r t i o n d e l i m i t s the micropyle.  Throughout develop-  ment the inner integument s t a i n s more i n t e n s e l y than the outer integument.  This feature, plus the smaller c e l l s , implies that the inner  integument adjusts to the increase i n s i z e of the ovule more by c e l l d i v i s i o n than by c e l l expansion. The outer integument i s two c e l l s t h i c k throughout except on i t s upper side at the c h a l a z a l region. (Fig.  In t h i s region there are two bumps  88), the r e s u l t of a few i n t e r n a l c e l l l a y e r s .  The bump nearest  the micropyle i s discerned very e a r l y , at the time when the megaspore mother c e l l i s d i f f e r e n t i a t e d ( F i g . 83). The one f u r t h e r away from the micropyle appears at the t e t r a d stage, through p e r i c l i n a l d i v i s i o n s i n the outermost c e l l l a y e r ( F i g . 86). The c e l l s of the outer integument are l a r g e r and more vacuolate than those of the inner integument.  Accomodation of the outer integu-  ment to i n c r e a s i n g ovule s i z e i s mainly through c e l l enlargement.  As  24  the ovule grows, the bumps increase i n s i z e .  The f i r s t bump (that i s ,  the one nearer the micropyle) assumes an i n v e r t e d cone shape ( F i g . 90). The second bump (that i s , the one f u r t h e r away from the micropyle) becomes a flange of t i s s u e adpressed against the f i r s t bump. bumps remain close t o the p o i n t of ovule attachment.  Both the  At the 8-nucleate  stage, the two bumps are so c l o s e l y adpressed that they appear as one s t r u c t u r e ( F i g . 91).  This s t r u c t u r e projects up i n t o the c l e f t between  the stylebranches ( F i g . 91a), and may, as has been postulated, (see True, 1893; Weier and Dale, 1960), d i r e c t p o l l e n tubes towards the micropyle.  The outer integument begins t o d i s i n t e g r a t e soon a f t e r  fertilization.  I t i s almost o b l i t e r a t e d by the time a 4 - c e l l embryo  i s developed. Nucellus Growth of the nucellus and r e - o r i e n t a t i o n of the ovule occur simultaneously.  During e a r l y megasporogenesis  an u p t i l t t o an orthotropous p o s i t i o n  the ovule i s pushed from  through d i v i s i o n s of the n u c e l l a r  c e l l s adjacent t o the megaspore mother c e l l ( F i g . 82).  Subsequent  d i v i s i o n s of the n u c e l l a r c e l l s around the megaspore, and l a t e r  around  the embryo sac, are o r i e n t e d at an angle t o the axis of the embryo sac ( F i g . 83). ovule.  This growth contributes to increase i n thickness of the  By the 8-nucleate stage, m i t o t i c a c t i v i t i e s o f these c e l l s cease  and the c e l l s elongate p a r a l l e l t o the l o n g i t u d i n a l a x i s of the embryo sac,  thereby i n c r e a s i n g the length of the ovule ( F i g . 91).  Some of the  c e l l s next t o the embryo sac are crushed by the transverse expansion of the l a t t e r .  25  The nucellar protoderm s t a r t s to divide p e r i c l i n a l l y at the l a t e megaspore mother c e l l stage ( F i g . 83).  By the 4-nucleate stage most of  the protodermal c e l l s have divided at l e a s t once.  Their  contribution  to the bulk of the ovule i s most obvious at t h i s stage ( F i g . 90). then on, as the ovule further increases  From  i n s i z e the protodermal c o n t r l -  bution becomes less obvious ( F i g . 91). Most of the growth of the nucellus i s a c t u a l l y due to a c t i v i t y i n the chalazal region.  Early growth i s i n length  ( F i g . 84).  Later growth i s  the outcome of c e l l d i v i s i o n s i n variously oriented planes, contributing to increase i n bulk of the ovule as well as s h i f t i n g the ovule to a hemianatropous p o s i t i o n (Figs. 85, 88, 91). the nucellar c e l l s mostly involves c e l l  Further d i f f e r e n t i a t i o n of  expansion.  Embryo sac The embryo sac i s of the Polygonum type (sensu Maheshwari, 1950). The archesporial c e l l i s d i f f e r e n t i a t e d as the megaspore mother c e l l before the f l o r e t i s extruded from the inflorescence sheath. shows a stage i n megasporogenesis.  Figure  84  The tetrad that i s formed i s usually  l i n e a r ( F i g . 85), but i s occasionally T-shaped ( F i g . 87).  The functional e  megaspore i s the chalazal one.  The f i r s t megaspore to degenrate i s  either the one above the chalazal megaspore, or the next one above.  The  chalazal megaspore i s the functional megaspore. The embryo sac undergoes changes i n shape as i t develops.  At the  2-nucleate stage i t i s oblong ( F i g . 89), and becomes broadly fusiform at the 4-nucleate stage ( F i g . 90).  At the beginning of the 8-nucleate stage  the micropylar end has broadened out so that the embryo sac appears  2 6  broadly ovate at t h i s end, while at the c h a l a z a l end i t abruptly narrows to a s l o t ( F i g . 91).  Just before f e r t i l i z a t i o n the s l o t widens ( F i g . 94).  The.embryo sac at t h i s stage i s ovate ( F i g . 94).  From t h i s stage on, i t  increases i n length (Figs. 97, 98). At the e a r l y 8-nucleate stage ( F i g . 91), i t i s hot p o s s i b l e to d i s t i n g u i s h the egg from the synergids. As the synergids d i f f e r e n t i a t e a large vacuole develops i n each of them at the lower (= c h a l a z a l ) end, and the nucleus i s at the upper (= micropylar) end ( F i g . 92).  No f i l i f o r m  apparatus i s seen i n the synergids. When the egg and the synergids have d i f f e r e n t i a t e d the antipodals have divided once ( F i g . 92).  The a n t i -  podals l i e i n the s l o t at the c h a l a z a l end of the embryo sac. cytoplasm i s dense, granular, and non-vacuolate.  Their  The polar n u c l e i at  t h i s stage are s i t u a t e d above the egg and synergids and are very c l o s e to them. Just p r i o r to f e r t i l i z a t i o n c e r t a i n v i s i b l e changes occur. cytoplasm of the synergids becomes dense and granular. decreases i n s i z e ( F i g . 94), and then degenerates.  One synergid  The antipodals have  p r o l i f e r a t e d even more and have moved to a l a t e r a l p o s i t i o n . of the antipodals are d i f f i c u l t to d i s t i n g u i s h . seen.  The  The o u t l i n e s  No m i t o t i c f i g u r e s were  Each antipodals appears to have one nucleus only.  The p o l a r n u c l e i  move away from t h e i r p o s i t i o n next to the egg and synergids to a higher p o s i t i o n i n the c e n t r a l c e l l .  Fertilization F e r t i l i z a t i o n occurs a f t e r one synergid has degenerated.  The p o l l e n  27  tube t r a v e l s through the micropyle and nucellus and seems to enter the embryo sac between the base of the p e r s i s t e n t synergid and the embryo sac w a l l ( F i g s . 96, 97).  The t i p of the p o l l e n tube appears to have a  deposit of a darkly s t a i n i n g m a t e r i a l . gametes was not seen.  Actual discharge of the male  I t could not be ascertained whether the p o l l e n  tube contents are discharged i n t o the synergid before entering the or are discharged d i r e c t l y i n t o the egg. m a t e r i a l s i s seen on top of the egg.  A quantity of chromatin-like  This may be p o l l e n tube contents  plus remnants of the degenerated synergid. before  egg,  The polar n u c l e i do not fuse  fertilization.  Post-fertilization This was studied up to the 4 - c e l l embryo stage.  The endosperm i s  free-nuclear and i n i t i a l l y develops f a s t e r than the embryo ( F i g . 98). The h i t h e r t o p e r s i s t e n t synergid begins to degenerate.  Oryzopsis hymenoides (Roem. and Schult.) R i c k e r A comparison of Oryzopsis hymenoides with 0. virescens w i l l be emphasized i n t h i s account.  F l o r e t organogenesis Organ i n c e p t i o n follows t h i s sequence: awn-lemma ( F i g . 99), palea and stamens ( F i g . 100), l o d i c u l e s and c a l l u s ( F i g . 101), gynoecial w a l l (Fig. 102), and f i n a l l y , the ovule ( F i g . 104).  Oryzopsis hymenoides  28  d i f f e r s from 0. virescens i n the precocious development of the c a l l u s and the e a r l y d i f f e r e n t i a t i o n of the awn-lemma j u n c t i o n . the gynoecial w a l l reaches  By the time  the p o s t e r i o r side of the f l o r e t apex the  awn-lemma j u n c t i o n and the c a l l u s are well-marked ( F i g . 103).  Further  development of the f l o r e t i s seen i n Figures 104 and 105.  F l o r e t a p i c a l meristem As i n 0. virescens there seems to be no inner t u n i c a i n 0. hymenoides (Figs. 99, 100).  The f l o r e t a p i c a l meristem a l s o becomes d i s p l a c e d and  r e - o r i e n t e d i n the course of f l o r e t development.  Awn-lemma I n i t i a t i o n of the awn-lemma primordium i s as i n 0. virescens ( F i g . 99).  Subapical a c t i v i t y i s involved i n the growth of the young primor-  dium ( F i g . 100), but c e s s a t i o n of t h i s a c t i v i t y occurs e a r l i e r than i n 0. v i r e s c e n s .  A shorter awn i n 0. hymenoides i s perhaps an expression  of the e a r l i e r cessation of subapical a c t i v i t y .  I n t e r c a l a r y growth  and c e l l u l a r d i f f e r e n t i a t i o n have produced a broader awn by the time of l o d i c u l e i n i t i a t i o n ( F i g . 106; c f . F i g . 19).  D i f f e r e n t i a t i o n of the  awn-lemma j u n c t i o n i s seen when the gynoecial w a l l i n i t i a t e s ( F i g . 107). This process i s comparable w i t h that seen i n 0. v i r e s c e n s .  Cells i n  the region of the presumptive j u n c t i o n are s m a l l , have dense cytoplasm, and undergo oblique d i v i s i o n s ( F i g . 108).  R e - o r i e n t a t i o n of d i v i s i o n a l  planes and continued d i v i s i o n s r e s u l t i n an expanded lemma apex which i s s i m i l a r to that i n 0. virescens except f o r two features: i n 0. hymenoides  29  fewer p e r i c l i n a l d i v i s i o n s occur i n the ground meristem; the a d a x i a l protoderm remains one-layered (Figs. 109, 110, 111). lemma are protodermal outgrowths.  Hairs on the mature  As i n 0. virescens the upper p o r t i o n  of the f r e e margins of the lemma i s longer than the p o r t i o n of the lemma attached to the awn and forms two 'ears' i n f r o n t o f the awn ( F i g . 105). At m a t u r i t y , where the awn base i s attached to the lemma apex, the c e l l s remain small ( F i g . 112). This zone presents a l i n e of weakness and accounts f o r the e a s i l y deciduous nature of the awn.  Callus The c a l l u s of 0. hymenoides d i f f e r s from that of 0. virescens i n i t s e a r l i e r development and i t s shape a t maturity.  But they are s i m i l a r i n  t h e i r i n i t i a l stages of development and i n t h e i r c e l l u l a r composition. I n i t i a t i o n occurs at the time that the l o d i c u l e s appear, and i s through expansion, v a c u o l a t i o n and d i v i s i o n of ground meristem c e l l s ( F i g . 113). At the base of the lemma on the a n t e r i o r s i d e , ground meristem c e l l s near the protoderm become vacuolate and enlarge, i n planes p a r a l l e l w i t h and perpendicular to the adjacent protoderm ( F i g . 113), forming a s l i g h t bulge outwards.  Continued c e l l enlargement of the ground meristem c e l l s ,  accompanied by p e r i c l i n a l and oblique d i v i s i o n s , increases the s i z e of of the bulge ( F i g . 114). The protoderm adjusts to t h i s increase i n s i z e by d i v i d i n g a n t i c l i n a l l y .  The c a l l u s shown i n Figure 114  i s at the  stage when the gynoecial w a l l i n i t i a t e s on the a n t e r i o r side of the f l o r e t apex.  I t i s comparable w i t h the c a l l u s of 0. virescens seen i n  Figure 27, which i s during the growth of the a n t e r i o r p o r t i o n of the  30  gynoecial w a l l .  During the e a r l y growth o f the a n t e r i o r p o r t i o n o f the  gynoecial w a l l i n 0. hymenoides, increase i n s i z e of the c a l l u s i s mainly through c e l l expansion, i n a d i r e c t i o n perpendicular to the adjacent protoderm ( F i g . 115). Further growth of the c a l l u s sees a s h i f t i n the d i r e c t i o n o f expansion o f the ground meristem c e l l s .  When the gynoecial  w a l l appears on the p o s t e r i o r side of the f l o r e t apex, expansion o f the c e l l s o f the c a l l u s i s predominantly i n a d i r e c t i o n p a r a l l e l w i t h the protoderm ( F i g . 116). Thus the c a l l u s i s distended downward instead o-f outward, as i n the e a r l i e r stages. dermal c e l l s begin to form h a i r s .  At the same time, some o f the protoContinued development o f the c a l l u s  involves extensive elongation of the ground meristem c e l l s , not only downward but a t an angle t o the adjacent protoderm, so that the c a l l u s grows downward and o b l i q u e l y outward (Figs. 117, 118, 119). The protodermal c e l l s at the t i p of the c a l l u s remain s m a l l , but those higher up on the c a l l u s extend l o n g i t u d i n a l l y to keep pace with the expansion of the ground meristem c e l l s .  When f u l l y formed, the c a l l u s has a  sharp pointed t i p , d i r e c t e d away from the v e r t i c a l axis of the f l o r e t (Figs. 105, 119). The a n t i - c l o c k w i s e t i l t i n g o f the f l o r e t - r a c h i l l a j u n c t i o n seen i n 0. virescens i s absent i n 0. hymenoides. For ease of comparison, a t a b l e i s given of the figures that i l l u s t r a t e comparable stages i n awn-lemma and c a l l u s development i n the two species, using gynoecium development as the standard of reference (Table I ) .  31  TABLE I. Reference table for comparison of stages in awn-lemma and callus development in 0. virescens and 0. hymenoides, using the stage of gynoecium development as a marker. The numbers refer to figures at the pertinent stages.  Stage of gynoecium development  0. virescens  0. hymenoides  awn-lemma  callus  awn-lemma  callus  Initiation of lodicules  19  19  106  113  Initiation of anterior gynoecial wall  20  26  107  114  Growth of anterior gynoecial wall  21  27  108  115  Gynoecial wall appears on posterior side of floret apex  22  28  109  116  Ring-shaped gynoecial wall  23  none  110  117  Prior to integument initiation  24  29  none  none  Initiation of inner integument on upper side  none  none  111  118  Complete inner integument  25  30  none  none  Ovule in orthotropous position  none  none  112  119  32  Palea Development of the palea in 0. hymenoides i s similar to that in 0. virescens (Figs. 120, 121, 122). At maturity the palea differs in the presence of elongate protodermal cells at the distal end (Figs. 123, 123a).  Lodicules No visible difference can be seen in the initiation of the posterior lodicule as compared with that in 0. virescens (Figs. 120, 121). However, the fully developed posterior lodicule i n 0. hymenoides i s relatively thicker and has a blunt distal end (Fig. 124;  c f . Fig. 38). This is  undoubtedly due to more c e l l division as development proceeds. The anterior lodicules initiate and develop as in 0. virescens (Fig. 125). At maturity they are uniformly thick structures with an acute abaxial tip (Figs. 126, 127, 128), unlike those i n 0. virescens which have an exceptionally thickened anterior portion (cf. F i g . 50).  Stamens Development of the stamens is as in 0. virescens, except for the presence of 'bearded anthers' in 0. hymenoides. The anther 'beard' consists of multicellular, uniseriate hairs formed from protodermal cells at the distal end of the anther . An early stage of development of these hairs is seen Figure 129.  33  Gynoecium This structure i n i t i a t e s and develops i n a s i m i l a r manner as described for 0. virescens (Fig. 130).  Figures 131 and 132 show that  that portion of the f l o r e t apex which remains a f t e r the i n i t i a t i o n of the ring-shaped  gynoecial wall continues  to grow as the ovule.  At  anthesis the inner margins of the ovary wall meet but do not fuse, so that the opening between the margins i s not completely as the s t y l a r canal (Figs. 113, 294, a region of smaller c e l l s —  295).  closed, but remains  Around the s t y l a r canal i s  this i s the 'stylar core'.  There are two s t y l e s , each formed from a l a t e r a l portion of the gynoecial w a l l . (Fig. 134;  The s t y l e s are closer here than they are i n 0. virescens  c f . F i g . 76).  The vascular supply of each s t y l e i s an exten-  sion of a l a t e r a l vascular bundle of the ovary ( F i g . 294).  The stigma-  t o i d tissue i n each s t y l e runs p a r a l l e l with the vascular bundle i n the style.  According  to Bonnett (1961), the stigmatoid tissue i n Avena  s a t i v a i n i t i a t e s i n the ovary wall above the f i r s t c e l l layer of the inner surface of the ovary wall and proceeds acropetally into the styles.  I n i t i a t i o n of stigmatoid tissue was  not studied by the author.  Figure 295 shows the p o s i t i o n of the stigmatoid tissue In the ovary w a l l .  Early ovule and embryo sac development Ovule The ovule of 0. hymenoides i s s i m i l a r to that of 0. virescens except for some s l i g h t differences i n s i z e .  The ovule i n 0. hymenoides at the  inner integument stage i s narrower ( F i g . 135).  At the 8-nucleate stage  34  i t i s a l s o not as wide a t the c h a l a z a l end ( F i g . 143b). Integuments Inception and development of the integuments does not d i f f e r much from that i n 0. virescens ( F i g s . 135 to 138). them are noted.  Some d i f f e r e n c e s between  The c h a l a z a l p o r t i o n of the outer integument i n  0. hymenoides d i f f e r s from that i n 0. v i r e s c e n s .  I n 0. hymenoides the  outer integument has only one bump i n the c h a l a z a l r e g i o n , whereas i n 0. virescens two bumps are present.  Whereas i n 0. virescens the two  bumps are adpressed to appear as one prominent bump which projects i n t o the c l e f t between the s t y l e branches and p e r s i s t s u n t i l a f t e r f e r t i l i z a t i o n , the s i n g l e bump i n 0. hymenoides i s poorly developed ( F i g . 141), and i t s t a r t s t o f l a t t e n out p r i o r to f e r t i l i z a t i o n ( F i g . 142). At the time of f e r t i l i z a t i o n the outer integument has already s t a r t e d to degenerate ( F i g . 143b). Nucellus Growth patterns i n the nucellus are s i m i l a r i n both species, except that there are more p e r i c l i n a l d i v i s i o n s i n the n u c e l l a r protoderm i n 0. virescens ( c f . F i g s . 142, 90). Embryo sac As i n 0. virescens there i s one a r c h e s p o r i a l c e l l i n 0. hymenoides. Megasporogenesis i s the same i n both species (Figs. 139, 140). The two species d i f f e r notably i n the shape o f the e a r l y embryo sac and i n the d i f f e r e n t i a t i o n of the synergids.  In 0. hymenoides the  embryo sac i s almost rectangular a t the 4-nucleate stage and i n the e a r l y 8-nucleate stage.  The c h a l a z a l s l o t that i s so c h a r a c t e r i s t i c of  35  the embryo sac i n 0. virescens i s absent i n 0. hymenoides.  At maturity,  but before f e r t i l i z a t i o n , the shape of both the embryo sacs becomes ovate (Fig. 143b). D i f f e r e n t i a t i o n of the egg v i s i b l y resembles that i n 0. virescens (Fig. 142a).  The mature u n f e r t i l i z e d egg i s highly vacuolate and also  lacks starch grains (Fig. 143a).  The d i f f e r e n t i a t e d synergids, instead  of possessing a large vacuole at the lower (= chalazal) end, as i s seen i n 0. virescens, have a number of scattered smaller vacuoles.  A  form apparatus develops i n each of the synergids.  fertiliza-  Even before  tion the two synergids are d i f f e r e n t from each other —  fili-  one degenerates anti  stains deeply, while the other becomes highly vacuolate and stains lightly. The polar n u c l e i and antipodals appear similar to those of 0. virescens.  Fertilisation This process appears to be d i f f e r e n t from that observed i n 0. virescens in two respects:  the presence of two synergids as opposed to one i n  0. virescens, and the discharge of the pollen tube contents into the degenerate synergid.  From s e r i a l sections of the f l o r e t shown i n  Figures 144a,b,c, chromatin-like bodies are seen i n the egg.  Also,  remnants of the p o l l e n tube can be found i n the degenerate synergid (Fig. 145a).  The sections examined seem to indicate that the p o l l e n  tube contents reach the egg v i a the degenerate synergid (Figs. 144a,b,c). The polar n u c l e i are not fused p r i o r to f e r t i l i z a t i o n .  36  Post-fertilization Observations were made up to the 2-cell embryo stage (Fig. 146). The hitherto persistent synergid begins to degenerate. Endosperm formation i s i n i t i a l l y free-nuclear.  DISCUSSION  General remarks about the interpretation of hlstogenetic data Histogenetic studies usually follow one or both of these approaches: 1. the vegetative shoot axis and/or the reproductive axis of one or more species are/is studied and the histogenetic data obtained are compared and used to deduce the phyllome or caulome nature of an organ; 2.  a broad comparative histogenetic survey is made of an organ-category  in as many species as possible (such as the study by Sprotte, 1940). The f i r s t method is by far the more popular and is the one used in this study (see Rohweder, 1963, for a critique of the method). It has to be borne i n mind that interpretative histogenesis has no vocabulary of i t s own but i s expressed in the language of comparative morphology. Moreover, concepts of organs such as ' l e a f , 'stem', 'lemma', and 'stamen' originate from comparative morphology. An illustration of these two statements is given in these words used to describe the development of the lemma, v i z . , the lemma is leaf-like.  To the author, this simply  indicates that the nature of the lemma can best be understood by comparing i t to a leaf.  Both organs f i t the c r i t e r i a of a phyllome. At no  37  time i s i t Implied that the lemma had been, at some stage i n the past, a l e a f which became modified i n t o a lemma.  To v i s u a l i z e the lemma as  having been derived from a f o l i a g e l e a f i s to replace a purely morphol o g i c a l concept by a h i s t o r i c a l concept  f o r the v a l i d i t y of which h i s t o -  genetic data provide no evidence. Any morphological i n t e r p r e t a t i o n of an organ on the b a s i s of i t s histogenesis has to be approached w i t h caution.  This i s e s p e c i a l l y  c r u c i a l when i s o l a t e d developmental observations are made on h i g h l y s p e c i a l i z e d s t r u c t u r e s , p a r t i c u l a r l y the stamens and c a r p e l s .  There i s  always the p o s s i b i l i t y of wrong inferences, as the developmental v a r i a t i o n w i t h i n these organs i s not w e l l known and has not been observed sufficiently.  The i n t e r p r e t a t i o n of the l e a f and the stem as being of  a phyllome and caulome nature r e s p e c t i v e l y can be made w i t h more c o n f i dence, e s p e c i a l l y i n the grasses. Leaf and bud development i n the Gramineae has been studied i n numerous species (Sharman, 1945; Pankow and Guttenberg, 1959).  In t h i s family the leaves have a shallow s i t e  of i n i t i a t i o n ( i n the t u n i c a ) , and show marginal growth.  In comparison,  the l a t e r a l shoot axes are e s t a b l i s h e d i n the deeper l a y e r s of the main axis ( i n the corpus), do not show marginal growth but approach a r a d i a l symmetry.  A l s o , a s h e l l zone i s present. Generally, leaves have a  shallow s i t e of i n i t i a t i o n , but there have been occasional reports i n other angiosperms i n which the l e a f i n i t i a t e s i n the deeper layers of the apex.  In I r i s germanica (Rudiger, 1939), p e r i c l i n a l d i v i s i o n s which  i n i t i a t e l e a f formation occur f i r s t i n the two outermost corpus before they occur i n the second t u n i c a l a y e r .  In Euphorbia l a t h y r i s (Soma,  38  1959), l e a f i n i t i a t i o n involves the two t u n i c a layers as w e l l as the outermost corpus l a y e r .  However, i n both cases, no account was  of a x i l l a r y bud i n i t i a t i o n . described.  given  Later growth stages of the l e a f were not  Rohweder (op. c i t . ) concludes from t h i s and Schnabel's work  (Schnabel, 1941, c i t e d by Rohweder) that i n 'diesem F a l l e verhalten s i c h die Blattprimordien i n sehr jungen Stadien a l s o ganz wie e i n Achsen-VP, um so mehr, a l s s i e anfanglich annahernd radiar-symmetrische darstellen'.  Gebilde  The w r i t e r f e e l s that caution i s as much i n place i n the  negation of the phyllome nature of a s t r u c t u r e as i n i t s a f f i r m a t i o n .  F l o r a l morphology Awn-lemma In i n i t i a t i o n and development the lemmas i n 0. virescens and hymenoides resemble leaves.  0.  That the lemma i s l e a f - l i k e i s a d e s c r i p -  t i o n that agrees with a l l the grass lemmas that have been described so f a r (Cannon, 1900; 1954;  P h i l i p s o n , 1934, 1935;  Barnard, 1955, 1957a;  Mehlenbacher, 1970; to a l l grass lemmas.  Bonnett, 1953, 1961;  Sharman, 1960a, 1960b;  Klaus,  Holt,  1966;  Maze et a l . 1971, 1972), and i s probably a p p l i c a b l e As c u r r e n t l y i n t e r p r e t a t e d , the lemma represents  a bract borne on the s p i k e l e t a x i s , s p e c i a l i z e d f o r flower p r o t e c t i o n , and i n the a x i l of which a r i s e s the r e s t of the grass  floret.  There have been numerous attempts i n the past to equate the component s t r u c t u r e s of the awn-lemma with those of the grass l e a f .  About a hundred  years ago, Van Tieghem propounded the view that when the lemma has a subterminal awn,  the awn i s equivalent to the grass blade, and the parts  39  of the lemma above and below the Insertion of the awn are the equivalents of the ligule and sheath respectively.  In those lemmas where the awn i s  terminal, the awn is considered as the blade, the whole of the lemma the sheath, and i t s lateral lobes, i f any, as stipules which by fusion are supposed to give rise to the ligule.  Philipson (1934), challenged this  interpretation and suggested that i n lemmas with abaxial awns, the awn does not represent the whole blade but only a part of the blade which has become separated from the main portion of the blade, and this main portion is represented by the median and terminal portion of the lemma. Recently an interesting parallel was drawn by Maze et a l . (1971), between the growth pattern of the awn-lemma of Stipa t o r t i l i s and Oryzopsis miliacea and that of the leaf of Oryza sativa (Kaufman, 1959). Certain growth phenomena i n the awn-lemma of S_. t o r t i l i s which were used for comparison with Oryza by Maze et a l . are also seen i n 0. virescens (viz., multiple periclinal divisions in the adaxial protoderm and ground meristem of the expanded lemma apex).  The author concurs with Maze et a l .  that the developmental similarity between the Oryza leaf and the awn-lemma of species of Stipa and Oryzopsis i s a reflection of the fact that plants are developmentally very simple, and that this similarity does not imply the derivation of one structure from the other. Furthermore, the awnlemma of the Stipeae is like a grass leaf i n that i t has a sheathing base (lemma), and an appendage (awn). It is highly questionable i f anything can be gained from trying to speculate what are the parts taken in the lemma by the various regions of the grass leaf. Whether any significance can be attached to the presence of a  40  multiple protoderm in the lemma apex of 0. virescens and the absence of such in 0. hymenoides cannot be answered in this study.  It does, however,  result in a fatter apex In 0. virescens.  Callus The term callus i s usually used for the hardened lower end of the lemma,(Hitchcock, 1951;  Pohl, 1968). Developmentally the callus is  formed by the downward projection of the base of the lemma. This observation agrees with the earlier observation of Weatherwax (1942), t on 0. hymenoides.  Maze et, a l . (1971) were non-commital as to the origin  of the callus. In some grasses, such as Heteropogon, Chrysopogon, the base of the spikelet at the point of i t s articulation with the rachilla forms a sharp projection which simulates the callus formed by the lower end of the lemma in Oryzopsis.  The sharp structure at the base of the spikelet is  also termed a callus. The development of 'spikelet calluses' has not been studied.  It is  possible that the development of 'spikelet calluses' and 'lemma calluses' might be different. A sharp callus, whether i t is a structure on the spikelet or the lemma, is an adaptation for dispersal by animals, by adhering to their skin or fur (Stebbins, 1956).  In the Gramineae, the  development of a similar mechanism for seed dispersal may involve d i f f e r ent original structures.  Another example is seen in the modification  into bristles for wind dispersal of awns in Aegilops umbellulata and much divided glumes in Sitanion (Stebbins, 1972).  41  Palea  Like the lemma, the palea initiates and develops i n the manner of a phyllome. Most workers interpret the palea as a bracteole borne on the floral axis, which, together with opposing lemma, encloses the grass flower. The lemma, palea, and the grass flower collectively form the grass floret.  Schuster (1910), postulated the homology of the palea  with two fused sepals, which, together with a hypothetical third sepal, formed the outer perianth series of the grass flower.  The example  cited by Schuster to support his hypothesis i s the extant South Amerigenus Streptochaeta, in which the palea is b i f i d almost to the base. On the basis of histogenetic data, the palea seems to f i t best the current interpretation as a bracteole.  Its phenetic similarity with  a prophyll has been discussed by Arber (1925, 1934), and Philipson (1934).  Lodicules Much controversy has centred on, and s t i l l does, the interpretation of the nature of the lodicules.  These structures have been variously  interpreted as bracts (Hackel, 1881), or modified perianth members (Rowlee, 1898; Schuster, 1910; Arber, 1934; Gould, 1968). Recent histogenetic studies have brought the following interpretations. Barnard (1955, 1957a) describes lodicules as 'appendages with a foliarlike origin developed on the axis of the flower primordium'. Bonnett (1953, 1961) reports that the anterior lodicules in Zea and Avena  42  initiate i n the corpus, below the unlseriate tunica, and hence are to be considered as modified stems. Mehlenbacher (1970) found that in Oryzopsis hendersoni the anterior lodicules are partially stem-like and partially leaf-like.  Maze et a l . (1971) contend that anterior  lodicules are 'de novo' structures and are not comparable with any other plant structures.  Moreover, Maze et a l . decry the interpretation  of the anterior lodicules as homologues of perianth members, or any other modified structures, on the grounds that such an interpretation would require the assumption that lodicules evolved from perianth or any other structures, and i n the process of evolution lost a l l their characteristic features. In view of the varying opinions on the nature of the lodicules, the author would like to discuss the interpretation of the lodicules i n some detail. Hackel (1881), considered the anterior lodicules to be lateral halves of a leaf alternating with the palea, the middle part of which rarely develops f u l l y .  The posterior lodicule when present was supposed  to continue the distichous arrangement of the palea and the anterior lodicules.  This interpretation has to depend on a distichous arrange-  ment of the lodicules, and cannot be upheld. The trimerous disposition of the lodicules i n grasses, especially i n the bamboos, has been demonstrated,  Barnard (1955, 1957a) regards the grass flower as a branch system  and categorizes the lodicules as foliar structures which are borne laterally on the main axis of the branch system. His interpretation of the lodicules as foliar structures is rather non-committal.  43  That the l o d i c u l e s are stem-like i s the conclusion Bonnett (1953, 1961) a r r i v e d at a f t e r some elegant studies on maize and oat.  This  i n t e r p r e t a t i o n i s based p r i m a r i l y on the deeper s i t e o f i n i t i a t i o n of the l o d i c u l e s . convincing.  Bonnett's t e x t - f i g u r e s i n t h i s connection are not  For example, i n h i s paper on maize i n 1953, Figure 15D  shows a l e a f - l i k e l o d i c u l e primordium w i t h p e r i c l i n a l d i v i s i o n s i n the protoderm; and i n h i s paper on oat i n 1961, Figures 13B and 17E show l e a f and l o d i c u l e i n i t i a t i o n r e s p e c t i v e l y , both with i n i t i a t i n g p e r i c l i n a l d i v i s i o n s i n the c e l l l a y e r beneath the protoderm. Maze et a l . (1971, 1972) contend that the majority of developmental features seen i n the a n t e r i o r l o d i c u l e s (= d o r s a l l o d i c u l e s i n the papers by Maze et a l . ) are unique and point to a 'de novo' o r i g i n f o r these structures.  The unique features c i t e d by Maze et a l . are: (1) the  a n t e r i o r l o d i c u l e s do not i n i t i a t e d i r e c t l y from the f l o r e t a p i c a l meristem, but, i n s t e a d , from the base of the developing stamens; (2)  they i n i t i a t e i n an area of some c e l l d i f f e r e n t i a t i o n ;  (3) i n i -  t i a t i o n i s spread over a considerable area as seen i n l o n g i t u d i n a l section;  (4) e a r l y growth i n the l o d i c u l e s i s the r e s u l t of m i t o t i c  a c t i v i t i e s over a considerable p o r t i o n of the organ ;  (5) the pattern  of marginal growth i n the a n t e r i o r l o d i c u l e s has not been described i n any other organ. The author disagrees w i t h the extreme I n t e r p r e t a t i o n of Maze e t a l . and w i l l review i n d e t a i l each of t h e i r above arguments.  (1) That the  a n t e r i o r l o d i c u l e s do not a r i s e d i r e c t l y from the f l o r e t a p i c a l meristem i s a consequence of the time of t h e i r i n i t i a t i o n —  they a r i s e l a t e r than  44  the stamens.  In other words, t h e i r inception i s c e n t r i f u g a l .  While a  c e n t r i p e t a l (= acropetal) sequence of organ inception occurs i n many of the f l o r a l apices studied so f a r , a c e n t r i f u g a l sequence has been reported i n several plant taxa (see, f o r example, Corner, 1946).  Cheung and  S a t t l e r (1967) report that i n Lythrum s a l i c a r i a c e n t r i f u g a l inception occurs i n the formation of not only one but three kinds of appendages, sepals, petals and stamens.  S a t t l e r (1967) c i t e s a few genera i n which  the petal primordium i s i n i t i a t e d on a common stamen-petal complex, so that a petal primordium does not always have to i n i t i a t e d i r e c t l y on the f l o r a l apex.  (2) This feature i s a d i r e c t c o r o l l a r y of (1) and  should not be considered.  (3) This argument i s based on a very l i m i t e d  number of observations (Stipa t o r t i l i s and Oryzopsis miliacea, Maze et a l . 1971;  S t i p a lemmoni, Maze et a l . , 1972), and i s not upheld by other  histogenetic studies, including the author's  ( c f . Figs. 40, 41, f o r  Oryzopsis virescens and F i g . 120 f o r 0. hymenoides). arundinacea  In Bambusa  (Barnard, 1957a, F i g s . 3, 5), and Avena s a t i v a  (Bonnett,  1961, Figs. 17 E,F), i n i t i a t i o n of the lodicules involves only two to three c e l l s i n the v e r t i c a l d i r e c t i o n .  (4) While this i s a v a l i d point  with respect to anterior l o d i c u l e growth i n those species of S t i p a and Oryzopsis that have been investigated by Maze ejt a l . and the author, there are no data on other grasses for comparison. Moreover, the limited observations a v a i l a b l e , as mentioned above, are on c l o s e l y r e l a t e d taxa, so that any generalization of the uniqueness of t h i s feature i s open to suspicion. also apply to (5).  (5) The same criticisms leveled at (4)  45  In the author's opinion, some of the 'unique' features that Maze et a l . describe are not so unique a f t e r a l l , and others are based on too l i m i t e d a sample.  Furthermore, the i n t e r p r e t a t i o n of Maze et a l . i s that  the p o s t e r i o r l o d i c u l e i s d i f f e r e n t from the a n t e r i o r l o d i c u l e . workers o f f e r three possible I n t e r p r e t a t i o n s on the basis of t h e i r h i s t o g e n e t i c structure; lost;  of the p o s t e r i o r  These  lodicule  s t u d i e s , v i z . , (1) as a 'de novo'  (2) as a f o l i a r s t r u c t u r e which i s i n the process of being  (3) as a f o l i a r s t r u c t u r e which i s i n the process of conversion  to an organ s i m i l a r to the a n t e r i o r l o d i c u l e s .  Again, a v a i l a b l e data  on p o s t e r i o r l o d i c u l e growth are too scanty to permit any g e n e r a l i z a t i o n of t h i s nature.  Moreover, i n the bamboos, such as Bambusa nutans(Arber,  1925), Arundinaria f a l c a t a (Rowlee, 1898), the a n t e r i o r l o d i c u l e s and and the p o s t e r i o r l o d i c u l e  are a l i k e i n s t r u c t u r e , and i t i s not u n l i k e l y  that the p o s t e r i o r l o d i c u l e i s h i s t o g e n e t i c a l l y s i m i l a r to the a n t e r i o r lodicules.  I t seems more l o g i c a l to the author to consider a l l l o d i c u l e s  as one whorl of f l o r a l appendages of one c l a s s . There are p e r i a n t h - l i k e features i n the a n t e r i o r l o d i c u l e s . are: (1) the i n i t i a t i o n of the a n t e r i o r l o d i c u l e s involves d i v i s i o n s i n the protoderm; organs;  These  periclinal  (2) the a n t e r i o r l o d i c u l e s are determinate  (3) development of the a n t e r i o r l o d i c u l e s involves marginal  growth. Histogenetic data do not preclude the i n t e r p r e t a t i o n of l o d i c u l e s as modified perianth s t r u c t u r e s , and the author prefers t h i s view. other hand, there are no h i s t o g e n e t i c support or negate t h i s view.  On the  data at present that unequivocally  The amount of information on g r a s s - f l o r e t  46  development i s very  scanty.  The d i f f e r e n c e i n form between the a n t e r i o r and p o s t e r i o r l o d i c u l e s i s perhaps r e l a t e d to t h e i r f u n c t i o n .  At anthesis, the a n t e r i o r l o d i c u l e s  become t u r g i d and f o r c e the lemma outwards. relegated to an i n s i g n i f i c a n t r o l e .  The p o s t e r i o r l o d i c u l e i s  I t Is i n t e r e s t i n g that protogyny  occurs i n c e r t a i n grass species, such as Anthoxanthum odoratum L. and Alopecurus pratensis L., i n which there are no l o d i c u l e s . Arber (1926, 1927, 1928, 1934) described structures intermediate between l o d i c u l e s and stamens i n c u l t i v a t e d plants of Cephalostachyum virgatum and i n w i l d p l a n t s of Schizostachyum l a t i f o l i u m . them as stamen-lodicules  She l a b e l e d  and commented that although the existence of  l o d i c u l a r stamens may not i n i t s e l f prove the perianth nature of the l o d i c u l e s , i t lends p r o b a b i l i t y to t h i s view, as i t i s not unusual to f i n d p e r i a n t h members associated with stamens.  Of course these unusual  s t r u c t u r e s could also be dismissed as t e t r a l o g i c a l organs of no importance. Although both Arber and Schuster  i n t e r p r e t e d the l o d i c u l e s as members  of an inner perianth s e r i e s , they d i f f e r e d i n t h e i r i n t e r p r e t a t i o n of the outer perianth s e r i e s . Arber's view i s that the outer perianth s e r i e s has been l o s t i n the e v o l u t i o n of the grass flower.  The reason she  postulated a b i s e r i a t e l o d i c u l a r s e r i e s was to b r i n g the grass flower c l o s e r to the t y p i c a l monocotyledonous f l o r a l diagram. that her f l o r a l diagram of the grasses  'merely formed  framework upon which t o arrange her ideas'.  She acknowledged a hypothetical  Schuster's views are extreme-  l y i n t e r e s t i n g and deserve more than the scant a t t e n t i o n that i s paid to  47  them. Schuster  suggested that the palea was  homologous to two outer perianth  members and that the t h i r d outer perianth member probably during the evolution of grasses formed the inner perianth.  disappeared  from their ancestral forms.  The l o d i c u l e s  In the evolution of the grass flower  the  lodicules became reduced i n structure as a r e s u l t of the enveloping the flower by the lemma. structures was  The formation of the l o d i c u l e s as  thickened  a l a t e r adaptation, brought about by the fusion of the  o r i g i n a l l y two separate paleas. enclosed.  of  As a r e s u l t , the flower became completely  Because of an a l t e r e d s i t u a t i o n , the l o d i c u l e s had adapted  to another function, and this was  to open the opposing lemma and  palea  by swelling. However i n t e r e s t i n g these two hypotheses are, i t has to be kept i n mind that they are speculative reconstructions of ancestral forms and have no f a c t u a l existence.  Stamens In the two species of Oryzopsis  studied, the histogenesis of the ==- r  stamens d i f f e r s from that of a f o l i a r structure.  The stamens have a  deeper s i t e of i n i t i a t i o n , and i n early stages of growth assume a globose form.  Also, i n stamen i n i t i a t i o n the protoderm undergoes a n t i c l i n a l  d i v i s i o n s only.  Similar developmental features have been reported i n  stamen histogenesis i n other grasses by Bonnett (1953, 1961), Holt (1954), Barnard (1955, 1957a), Mehlenbacher (1970), and Maze e£ a l . (1971, 1972).  Maze et a l . also report the presence of a s h e l l zone i n  48  stamen formation in Stipa t o r t i l i s and Oryzopsis miliacea. consider the stamens to be stem-like i n grasses.  These workers  Stem-like stamens have  also been reported by Satina and Blakeslee in Datura (1943), by Barnard in Carex. Scirpus and Cyperus (1957b), i n Juncus and Luzula (1958), and in Stypandra and Bulbine i n the Liliaceae (1960). Various other workers, among whom may be mentioned McCoy (1940), Boke (1949), Tepfer (1953), Tucker (1959), Cheung and Sattler (1967), and Singh and Sattler (1972), consider stamens to be leaf-like.  The stamens  in question were found to initiate in the same layers as perianth members and carpels. Stamens in Downingia bacigalupii (Kaplan, 1968), and Hordeum distichon (Klaus, 1966), initiate beneath the superficial layers of the f l o r a l meristem, but have been interpreted as morphologically of a phyllome nature. The exact significance of these contradictory findings i s not clear. One could as easily argue for leaf-like stamens as for stem-like stamens. It i s interesting to note thatMerxmulIer and Leins (1967) have shown that in Sisymbrium strictissimum members of the same set of appendages (in this case stamens), may be initiated in different c e l l layers.  Histo-  genetic data for stamen development in the grasses studied so far support a cauline interpretation for grass stamens.  Gynoecium The unilocular ovary of the grass flower has often been interpretated as either unicarpellate or tricarpellate.  Among those who have upheld  49  the tricarpellate condition may be mentioned Schuster (1910), Arber (1934), Hitchcock (1951), and Gould (1968). Among adherents of the opposite view are Hackel (1889), Bews (1929), and Pilger (1954). Proponents of the tricarpellate condition consider the vasculature of the gynoecium and the presence of three styles i n some grass flowers as evidence of three fused carpels.  In most grass gynoecia four vascu-  lar bundles are present, one posterior, one anterior and two l a t e r a l . The anterior and the lateral bundles each represents the midrib of one carpel supposedly.  The posterior bundle supplies the ovule and i s  interpreted as the fused lateral bundles of the lateral carpels. Such a tricarpellate gynoecium would f i t in 'nicely' with the basic trimerous plan of the monocotyledonous flower. Developmental studies have not upheld this interpretation.  The  gynoecial wall in those grasses studied by Bonnett (1953, 1961), Holt (1954), Sharman (1960b), Klaus (1966), Mehlenbacher (1970) and Maze et a l . (1971, 1972) initiates as a single leaf-like structure.  The  author's observations in Oryzopsis virescens and 0^ hymenoides agree with the interpretation of these workers. Barnard (1957a) has suggested that the grass gynoecium consists of four carpels, one anterior, two l a t e r a l , and one posterior.  It is Barnard*e  Barnard's opinion that different parts of the gynoecial wall initiate at different levels and at different times, and that the different parts of the gynoecial wall represent different carpels.  The morphologically lowest  is the anterior carpel, the second i s the posterior carpel, and the two  50  lateral carpels are the most d i s t a l .  Barnard's claim is not substantiated  by evidence and has been rejected by later workers. With the exception of Barnard, a l l students of grass-floret histogenesis interpret the gynoecial wall as a single, continuous, leaf-like structure.  But the relation between the gynoecial wall and the  ovule i s a hotly debated issue.  The question i s :  Are grass ovules terminal  (stachyosporous), or are they borne on the gynoecial wall (phyllosporous)? In Oryzopsis virescens and 0. hymenoides the formation of the gynoecial wall does not use up the whole floret apex. The residual floret apex is gradually transformed into an ovule.  These observations  correspond with the observations of Holt (1954), Bonnett (1953, 1961), Sharman (1960b), Pankow (1962), Mehlenbacher (1970), and Maze et a l . (1971, 1972), a l l of whom interpret the grass ovule to be terminal on the floret axis.  A corollary of this interpretation is that the  concept of 'carpel' no longer applies to the grass gynoecium, since a carpel i s defined as a phyllome that bears ovule(s).  The point at  issue is the criterion by which an organ may be judged to be terminal. This question is discussed in some detail in connection with the author's review of Klaus' work, as i t concerns Klaus' interpretation of the grass gynoecium. According to Klaus, in Hordeum distichon L. the gynoecial wall arises as a peltate carpel and the ovule is borne on the 'cross-zone' ('querzone') of the carpel (see T r o l l , 1939, for terminology).  The  f l o r a l apex i s nearly used up in the formation of the carpel, that i s , the carpel is nearly terminal. The grass gynoecium is phyllosporous.  51  In view of the controversial reports of phyllospory versus  stachyospory  not only in the Gramineae but also in other Angiosperms (see, for example, Barnard, 1957b; Schultze-MoteL, 1959; Eckardt, 1957;  and  Pankow, 1962), the author w i l l discuss Klaus' work in some detail and attempt to resolve the contorversy. Two points are involved:  Where the gynoecial wall arises and  whether a floral apex remains after gynoecial wall i n i t i a t i o n .  Klaus'  statement that the floret apex is nearly used up in the formation of the gynoecial wall is very vague. The fate of the residual apex is not mentioned. His illustrations contradict his interpretation (see Klaus, 1966, Abb. 37, 38, 39).  In the formation of a terminal, or  nearly terminal, gynoecial wall, the corpus of the floret apex shows increased mitotic activity, and many c e l l divisions are seen in the apical surface i n i t i a l s (Brooks, 1940; Tucker and Gifford, 1966a, 1966b). Both features are not manifested in Hordeum distichon.  A floret apex  remains after gynoecial wall formation, and i t is gradually transformed into an ovule.  If one follows Buder's criterion (1928) that for an  organ to be considered terminal, i t must develop from apical i n i t i a l c e l l s , then the grass ovule is terminal. The presence of a cross-zone ('querzone') in the grass gynoecial wall is highly questionable.  According to continental European  literature, the development of the Angiosperm carpel (sensu lato) is similar to the development of a peltate leaf, and where the marginal meristems of the carpel meet, they form a transverse meristem, the cross zone. Whether the 'querzone' is something new, or an extension of the marginal meristems, i t is not identifiable in the two grasses  52  studied by the author.  An a n a l y s i s of the development of the  w a l l w i l l explain why.  The gynoecial w a l l i s a c t u a l l y i n i t i a t e d  an e n c i r c l i n g row of i n i t i a l s on the f l o r a l apex.  gynoecial by  These i n i t i a t i n g  d i v i s i o n s s t a r t on the a n t e r i o r side and progress to the p o s t e r i o r side.  Growth of the gynoecial w a l l outwards as a l a t e r a l appendage  occurs very e a r l y and i s greatest at the point where the d i v i s i o n s f i r s t appear, that i s , on the a n t e r i o r s i d e .  initiating This growth,  which i s mainly through a p i c a l a c t i v i t y , occurs simultaneously with  the  spread of the e n c i r c l i n g i n i t i a t i n g d i v i s i o n s around the flanks of the f l o r a l apex.  When the i n i t i a t i n g d i v i s i o n s reach the p o s t e r i o r side  of the f l o r a l apex, the shape of the gynoecial w a l l may a c y l i n d e r that has been cut diagonally i n h a l f .  be l i k e n e d to  From then on,  p o s t e r i o r rim shows a c t i v e a p i c a l a c t i v i t y and the gynoecial grows upwards as a tube.  the  wall  In t h i s sequence of events, i s there anything  which can be s a i d to fuse? The grass gynoecium i s i n t e r p r e t e d by the author as a u n i t s t r u c t u r e which develops from a s i n g l e gynoecial primordium and which encloses a terminal ovule.  I t i s i n f a c t a c a r p e l l a t e ( S a t t l e r , personal communication).  Embryo sac development The ovule i s hemianatropous, bitegmic and  pseudocrassinucellar.  The embryo sac i s of the monosporic, 8-nucleate type.  The  antipodals  p r o l i f e r a t e soon a f t e r the mature 8-nucleate embryo sac i s formed.  These  observations i n Oryzopsis virescens and 0. hymenoides are s i m i l a r to those described by Brown (1949), i n S t i p a l e u t o t r i c h a , and Mehlenbacher  53  and Maze ejt a l . in species of Stipa and Oryzopsis. This seems to be the usual type of embryo sac development in the Gramineae (Davis, 1966). The only grasses that do not follow this pattern of embryo sac development are those of the Bouteloua curtipendula (Michx.) Torr. complex, described by Mohamed and Gould (1966).  In these grasses, embryo sac  development is of the Adoxa type, and the antipodals do not proliferate. The number of bumps in the outer integument is interesting. The presence of one bump in the outer integument in the chalazal region has been reported in Stipa hendersoni (formerly known as Oryzopsis hendersoni Vasey) by Mehlenbacher in 1970, i n 1970), S. lemmonii (Maze et a l . , 1972) and In 0. hymenoides, one bump is present.  t o r t i l i s (Maze et a l . , elmeri (Maze and Bohm, 1973).  In 0. virescens there are two  bumps, and in the only other species of Oryzopsis studied, 0. miliacea, there are also two bumps. Fertilization in the two species appears to be different. In 0. virescens no filiform apparatus is seen. The synergids degenerate in  before f e r t i l i z a t i o n , but in those florets examed, one synergid persists in a degenerate form until f e r t i l i z a t i o n .  The site of pollen  tube enbry seems to be between the persistent synergid and the embryo sac wall.  In 0. hymenoides, in which each synergid has a distinct  filiform apparatus, the behavior of the synergids prior to f e r t i l i z a tion is different.  One synergid decreases in size, becomes densely-  staining and degenerates, while the other becomes highly vacuolate and shows no visible signs of degenerating. the 2-cell proembryo stage.  Both synergids persist until  The pollen tube enters the embryo sac  54 via the degenerate synergid. The entry and discharge of the pollen tube into one of the synergids has been demonstrated for Vallisneria (Wylie, 1941), Zea (Diboll, 1968), Gossypium (Jensen and Fisher, 1968) and species of Stipa.  Of these examples, a l l but  Vallisneria have synergids in each of which a filiform apparatus is present.  On the other hand, in Cardiospermum halicacabum (Kadry, 1946),  each synergid has a distinct filiform apparatus but the pollen tube enters the embryo sac between the synergids and the sac wall.  CONCLUSION * n Oryzopsis virescens and 0. hymenoides histogenesis of the lemma, palea, posterior lodicule and the gynoecial wall is similar, and indicates their foliar nature.  The anterior lodicules differ from  them in having a deeper initiation s i t e .  The interpretation of the  anterior and posterior lodicules as reduced perianth structures rather than as structures 'de novo' is preferred. Developmentally the stamens are stem-like. The gynoecium consists of a unit gynoecial wall surrounding a terminal ovule.  There are two styles, each of which  develops from the lateral portions of the gynoecial wall.  The grass  gynoecium may be considered acarpellate. Embryo sac development is of the monosporic, 8-nucleate type.  55  PART II Comparative developmental studies of the floret and embryo sac i n Oryzopsis virescens, 0. hymenoides, 0. micrantha, 0. k i n g i i , and 0. asperifolia.  INTRODUCTION The problems of circumscribing the genus Oryzopsis have been discussed in the general introduction.  The systematic disposition  of the five species studied is briefly reviewed here. Oryzopsis virescens (n = 12; Avdulov, 1928, as cited by Darlington and Wylie, 1955; Johnson, 1945a), i s an Eurasian species and belongs to the Old World section Piptatherum. Its floret characters, which are described i n PART I, (Figs. 1, 2, 3), f i t in well with those features which are generally employed to set Oryzopsis apart from Stipa. Oryzopsis hymenoides (n = 24, Johnson, 1945a) is in the North American section Eriocoma.  It was originally known as Stipa hymenoides  Roem. and Schult. (see Syst. 2: 339, 1817, for description). The generic transfer to Oryzopsis was proposed by Ricker, and was formally presented by Piper in 1906 (see volume I I , page 109, U.S. Natl. Herb. Contrib., 1906). This species is widespread in arid areas throughout western North America.  It resembles 0. virescens in i t s open panicle  and i t s indurate lemma, but i t is distinctively set apart from 0. virescens by i t s sharp callus and densely villous lemma (Figs. 4, 5, 6). A sharp callus and a villous lemma are features that are used to distinguish Stipa from most species of Oryzopsis.  Moreover, 0. hymenoides  56  crosses spontaneously with various species of Stipa.  To date, such  hybrids i n v o l i n g eleven d i f f e r e n t species of S t i p a have been reported (Johnson, 1972,  and the references therein). No other species of  Oryzopsis i s known to hybridize with Stipa.  One other supposed case  of intergeneric h y b r i d i z a t i o n , Oryzopsis hendersoni x S t i p a lemmoni, reported hy Spellenberg and Mehlenbacher (1971), i s i n f a c t , not  such.  Oryzopsis hendersoni Vasey i s more c l o s e l y a l l i e d to Stipa than to Oryzopsis, (Mehlenbacher, 1970).  In the j o i n t p u b l i c a t i o n of  Mehlenbacher made a formal transfer of the species to Stipa.  1971, According  to Sheerer and Johnson (1968), 0. contracta (B.L.Johnson) Shechter may have evolved through h y b r i d i z a t i o n between 0. hymenoides and micrantha.  0.  No other i n t e r s p e c i f i c crosses have been reported i n  Oryzopsis. Oryzopsis micrantha, 0. k i n g i i and 0. a s p e r i f o l i a are North American species and are placed i n the New  World section Oryzopsis.  The f i r s t two species are diploids (n = 11; Johnson, 1945a), while the t h i r d one i s a p o l y p l o i d (n = 23; Johnson, 1945a).  Bowden (1960)  reported a chromosome count of 2n = 48 for 0. a s p e r i f o l i a . micrantha  Oryzopsis  i s known to occur i n B r i t i s h Columbia, Alberta, Montana,  North Dakota, south to Nebraska, Oklahoma, New Mexico, Arizona and Nevada.  Oryzopsis k i n g i i has a very r e s t r i c t e d d i s t r i b u t i o n .  It  i s endemic to the meadows at high a l t i t u d e s i n the central S i e r r a Nevada mountains i n C a l i f o r n i a .  Oryzopsis a s p e r i f o l i a occurs from  Newfoundland to B r i t i s h Columbia, Maine to the Dakotas, including the Great Lakes region, and i n the Rocky Mountains from Montana to New  Mexico (Hitchcock, 1969).  57  The f l o r e t of 0. micrantha has an obovate glabrous lemma which i s f a i r l y indurate, an i n d i s t i n c t c a l l u s and a weak, untwisted and deciduous awn (Figs. 147, 148, 149).  With respect to these features  0. micrantha approaches the section Piptatherum.  However, the major  a f f i n i t y of this species, as discussed by Johnson (1945a), i s to the section Oryzopsis.  Oryzopsis k i n g i i may be described as a 'borderline  species' between Oryzopsis and Stipa.  As indicated by the Synonymy  i n Hitchcock (1951), 0. k i n g i i was o r i g i n a l l y described by Bolander i n 1872 as a Stipa, and was l a t e r transferred to Oryzopsis by Beal i n 1896.  I t i s so closely a l l i e d to Stipa on most characters that  i t s assignment to either Oryzopsis or S t i p a i s largely a r b i t r a r y . Its narrow non-indurate lemma, with a sharp c a l l u s and a strong, twisted geniculate awn (Figs. 150, 151), and i t s narrow panicle and slender involute leaves are strongly suggestive of Stipa.  Oryzopsis  micrantha and Oryzopsis k i n g i i represent the morphological extremes of the section Oryzopsis. Piptatherum  At one end, 0. micrantha presents some  features, c h i e f l y through i t s resemblance to 0. miliacea.  At the other end, 0. k i n g i i grades into Stipa.  Not s u r p r i s i n g l y ,  this d e f i n i t i o n of the section Oryzopsis has caused some uncertainty about the sectional and generic i d e n t i t y of certain species. Oryzopsis a s p e r i f o l i a has the largest f l o r e t as compared to the other four species.  The f l o r e t has a fusiform lemma which i s convolute,  a swollen, blunt, pubescent c a l l u s and a s t r a i g h t deciduous  awn (Figs.  152, 153, 154). I t i s reputed to be an a l l o t e t r a p l o i d , and i t s combination  of Piptatherum characters (weak and flexuous awn, many-  nerved glumes, broad f l a t leaves, f a i r l y indurate lemma) and Oryzopsis  58  features (glumes equal i n length to lemma, f i r s t glume shorter than second glume) i s used as an i n d i c a t i o n of i t s hybrid o r i g i n  (Johnson,  1945a). Developmental  data have not been incorporated into the systematic  studies of the genus Oryzopsis.  Recent work by Mehlenbacher (1970)  on Stipa hendersoni (Vasey) Mehlenbacher, and by Maze et a l . (1971, 1972) on 0. miliacea, S_. t o r t i l i s , and S.  lemmoni has showen that  developmental data can add another facet of evidence towards a better understanding of Stipa and Oryzopsis.  It i s hoped that data from the  present study, together with such developmental  data on other species  of Stipa and Oryzopsis as are a v a i l a b l e , can be used e f f e c t i v e l y as an adjunct to other c h a r a c t e r i s t i c s i n delimiting and working out the taxonomy of Oryzopsis. mental data.  There are c e r t a i n advantages to using develop-  Studies of f l o r a l histogenesis lead to a better under-  standing of the morphological features of the mature f l o r e t , for the mature form i s the r e s u l t of developmental processes.  The analysis  of growth patterns, i n the early stages of development of a structure, provide more features for comparison.  In mature structures early  growth patterns, which are due to the frequency and plane of c e l l d i v i s i o n , are usually o b l i t e r a t e d by the c e l l enlargement  phase of  growth.  MATERIALS AND METHODS The preparation of materials for study i s as described i n PART I for 0. virescens and 0. hymenoides.  Materials of 0. micrantha and 0.  a s p e r i f o l i a were c o l l e c t e d from transplants growing i n the experimental  59  p l o t s at the U n i v e r s i t y of B r i t i s h Columbia. and 0.^asperifolia  Plants of 0. micrantha  were o r i g i n a l l y from Marble Canyon P r o v i n c i a l Park  and Williams Lake r e s p e c t i v e l y ; both l o c a t i o n s are i n B r i t i s h Columbia. F l o r e t s of 0. k i n g i i were c o l l e c t e d from the high meadows i n Yosemite National Park, C a l i f o r n i a .  Some l i v e plants are maintained i n the  afore-mentioned experimental p l o t s .  Voucher specimens of a l l  five  species are deposited i n the Vascular Plant Herbarium of the Botany department, U n i v e r s i t y of B r i t i s h Columbia.  O r i e n t a t i o n of the sections  follows that used i n PART I .  OBSERVATIONS Oryzopsis micrantha ( T r i n . and Rupr.) Thurb. F l o r e t organogenesis The awn-lemma primordium i s the f i r s t s t r u c t u r e to appear on the f l o r e t a p i c a l meristem (Figs. 155, ,56).  This i s followed by the  palea and the stamens, which i n i t i a t e at the same time. of the l o d i c u l e s occurs next ( F i g . 157).  Initiation  The c a l l u s and the gynoecium  are the l a s t structures to appear (Figs. 158, 159).  The sequence of  i n i t i a t i o n of the f l o r a l parts p a r a l l e l s that i n 0. v i r e s c e n s .  F l o r e t A p i c a l Meristem The f l o r e t apex has a one-layered t u n i c a ( F i g . 155).  As i n 0.  virescens and 0. hymenoides, the f l o r e t apex i n 0. micrantha undergoes a displacement and r e - o r i e n t a t i o n i n the course of f l o r e t  development.  E a r l y i n f l o r e t development, the f l o r e t apex i s o r i e n t e d more or l e s s p a r a l l e l with the f l o r e t a x i s (Figs. 155, 156).  With the i n i t i a t i o n  60  of the anterior stamen, the f l o r e t apex i s deflected away from the axis to the posterior side of the f l o r e t (Fig. 157). The f l o r e t apex continues to be p o s t e r i o r l y directed during early growth of the anterior portion of the gynoecial wall  (Figs. 158, 159). After  i n i t i a t i n g d i v i s i o n of the gynoecial wall have e n c i r c l e d the f l o r e t o apex (Figs. 160, 181), the f l r e t apex continues growth as the ovule (Figs. 161, 182), but i t becomes re-oriented to an a n t e r i o r l y - d i r e c t e d  to a v e r t i c a l , and then  position.  Awn-lemma I n i t i a t i o n and early development of the awn-lemma primordium i s -  s i m i l a r to that i n 0. virescens (Figs. 155, 156). D i f f e r e n t i a t i o n of the awn-lemma junction i s f i r s t indicated by a c o n s t r i c t i o n which i s the r e s u l t of greater c e l l expansion i n the awn base than i n the lemma apex (Figs. 158, 159). P e r i c l i n a l d i v i s i o n s occur i n the ground meristem on both the abaxial and adaxial sides of the lemma apex, forming an expanded lemma apex (Figs. 163, 164, 165). The proportion of the lemma to the rest of the f l o r e t (excluding the awn) changes drastically  as the f l o r e t develops.  Prior to, and up t i l l , the  i n i t i a t i o n of the anterior portion of the gynoecial w a l l , the lemma i s relatively  small and leaves the d i s t a l h a l f of the f l o r e t exposed  (Figs. 158, 159). By the time the ring-shaped gynoecial wall i s formed, the lemma has extended to just above the top of the stamens (Fig. 160). Further growth of the f l o r e t sees extensive elongation of the lemma, as i t overtops, (Fig. 161), and encloses, the rest of the f l o r e t (Fig. 162). These observations are s i m i l a r to those  6 1  described for 0. virescens and 0. hymenoides.  The upper portions of  the free margins of the lemma increase in height more than the expanded lemma apex, and form two 'ears' in front of the awn (Figs. 161, 166). They are, however, smaller than the free 'ears' i n 0. virescens. The mature lemma apex resembles that of 0. virescens i n i t s double-convex shape and the presence of periclinal divisions i n the abaxial and adaxial ground meristem, but the resemblance is somewhat superficial.  In 0. micrantha (Fig. 167), the abaxial convexity i s  the result of ground meristem cell expansion rather than considerable periclinal divisions.  In the adaxial ground meristem, periclinal  divisions are not as extensive as i n 0. virescens.  Unlike 0. virescens,  the adaxial protoderm has only a few isolated periclinal divisions (Figs. 165, 166, 167). At the point of attachment of the awn to the lemma, the cells are much smaller than the cells in the awn base and the lemma apex (Fig. 167).  Callus Initiation of the callus i s through periclinal divisions and cell enlargement in the ground meristem at the base of the lemma on the anterior side (Fig. 168). As in 0. virescens, ground meristem tissue forms the bulk of the callus (Fig. 173). Early growth of the callus involves the expansion and vacuolation of the ground meristem c e l l s , in a direction perpendicular to the adjacent protoderm, forming a rounded protuberance (Figs. 169, 170). This i s accompanied by c e l l expansion in the adjacent protoderm (Fig. 170). At the time of initiation of the inner integument, the ground meristem cells i n the  62  middle section of the c a l l u s on the anterior side begin to expand obliquely, that i s , inward and at an angle to the adjacent protoderm (Fig. 171).  The protodermal and ground meristem c e l l s at the d i s t a l  end of the c a l l u s , near the a x i l of the lemma, expand i n a l o n g i t u d i n a l d i r e c t i o n , pushing the c a l l u s downward ( F i g . 172).  At the same time,  the protodermal and ground meristem c e l l s i n the basal portion of the c a l l u s continue to expand obliquely, toward the axis of the f l o r e t (Figs. 172, 173).  Consequently, the c a l l u s grows downward and inward,  forming a rounded t i p (Figs. 172, 173).  As i n 0. virescens the  f l o r e t - r a c h i l l a t i l t s i n an anti-clockwise 168, 169 and 171).  d i r e c t i o n (compare Figs.  The t i l t i n g i s not as extreme as i n 0. virescens  so that the rounded t i p of the c a l l u s i n 0. micrantha i s l a t e r a l l y directed and does not l i e on the v e r t i c a l axis of the f l o r e t (Fig. 162). Two growth feactures seen i n 0. micrantha but not i n 0. virescens involve the protoderm of the c a l l u s and the r a c h i l l a .  Some of the  protodermal c e l l s of the c a l l u s on the anterior side undergo random p e r i c l i n a l , oblique and a n t i c l i n a l d i v i s i o n s at a time when the f l o r e t undergoes extensive  elongation growth (Figs. 171, 172, 173).  The  protoderm of the r a c h i l l a on the posterior side elongates a n t i c l i n a l l y to produce a s l i g h t projection ( F i g . 173).  Palea Development of the palea i n 0. micrantha i s s i m i l a r to that i n 0. virescens, except that i n 0. micrantha the palea does not have a b i s e r i a t e d i s t a l portion (Figs. 174,  175).  63  Lodicules Initiation and growth of the lodicules is similar to that in 0. virescens. Stages in lodicule development are shown in Figures 176, 177, 178 and  179.  Stamens The development of the stamens in 0. micrantha and in 0. virescens is remarkably similar.  A description of stamen development in 0.  micrantha would be repetitious.  Gynoecium Early stages in the development of the gynoecium are shown in Figures 180, 181.  The ovule is terminal, and the gynoecial wall grows  upward as a tube (Figs. 181, 182).  The lateral sides of the gynoecial  wall give rise to a style branch each (Fig. 183).  The style branches  are closer together in 0. micrantha than they are in 0. virescens, (Fig. 185; cf. Fig. 76).  Proliferation of tissues ('stylar core') on  the inner margins of the ovary wall brings the margins together (Figs. 184, 184a). The inner margins come in contact but do not fuse, so that the opening between the inner margins is not completely closed but remains as the stylar canal (Fig. 184).  Ovule and embryo sac development Integuments The inner integument is f i r s t seen on the upper side (Fig. 183). At this stage, the archesporial c e l l is not distinguishable. When the  64  inner integument appears on the lower side, the single-celled archesporium is distinguished by i t s larger size and i t s denser cytoplasm (Fig. 186). The outer integument i s also f i r s t visible on the upper side (Fig. 187).  In the chalazal region of the outer integument, a  single prominent bump is formed (Figs. 189, 191). The outer integument starts to degenerate prior to f e r t i l i z a t i o n . Nucellus and embryo sac development Growth patterns in the nucellus leading to increase in size of the ovule and its orientation to a hemianatropous position are similar to those observed in the previous species (Figs. 188, 191, 192).  Oryzopsis  micrantha is like 0. hymenoides in that there are few periclinal divisions in the nucellar protoderm. In megasporogenesis, a linear tetrad is more commonly found than a T-shaped one.  In the linear tetrad the f i r s t megaspore to abort is  the micropylar.  In the T-shaped tetrad, both the micropylar megaspores  degenerate at the same time and are the f i r s t ones to do so.  Inter-  mediate stages i n megagametogenesis are seen in Figures 190 and 191. The synergids have a filiform apparatus each (Fig. 193). They remain densely cytoplasmic throughout their growth (Figs. 193, 194). Starch granules are seen in the egg before f e r t i l i z a t i o n (Fig. 193a). Crystals are present i n the nucleoli of the polar nuclei (Fig. 193). The polar nuclei fuse before f e r t i l i z a t i o n .  Fertilization It was very d i f f i c u l t to trace the path of the pollen tube into the embryo sac. Both the synergids appear to degenerate at  65  fertilization.  One decreases  i n size more than the other.  Chromatin-like  bodies are seen i n the larger degenerate synergid (Figs. 195, 195a).  This  seems to indicate that the pollen tube contents enter the egg v i a one synergid.  Post-fertilization I n i t i a l l y the endosperm i s also nuclear.  Oryzopsis k i n g i i (Boland.) Beal Floret organogenesis The f l o r e t a p i c a l meristem, with a one-layered tunica, f i r s t i n i t i a t e s the awn-lemma (Fig. 197). This i s followed by the appearance of the palea and the stamens (Fig. 198). The lodicules are the next structures to develop, and during their early gorwth (Fig. 199), but before the gynoecium i n i t i a t e s , the callus and the awn-lemma junction become evident (Figs. 205, 212). The gynoecium i s the l a s t structure to i n i t i a t e (Fig. 200). Changes i n the shape of the f l o r e t during growth are shown i n Figures 201 to 204.  As i n the other three species  described previously, In 0. k i n g i i the f l o r e t a p i c a l meristem undergoes a displacement  and r e - o r i e n t a t i o n i n the course of f l o r e t development  (cf. F i g s . 200, 201, 203, 204). Concurrently, there i s a change i n the porportion of the lemma to the rest of the f l o r e t  (excluding the awn).  66  Awn-lemma The awn-lemma primordium in i t s initiation and early growth i s similar to that i n the previous species.  Differentiation of the  awn-lemma junction starts early and is indicated by periclinal divisions and c e l l expansion i n the adaxial ground meristem of the lemma apex (Figs. 205, 206, 207, 208).  On the abaxial side the protoderm is  one-layered, while some cells in the ground meristem may divide periclinally once (Fig. 209).  The mature lemma apex is quite different  from that of 0. virescens, 0. hymenoides and 0. micrantha.  Instead  of a biconex shape as present in the other three species, the lemma apex of 0. kingii has a convex adaxial surface and a staight abaxial surface (Fig. 211).  The adaxial convexity results from a combination  of the expansion of the protodermal cells i n an anticlinal direction, and periclinal divisions in the ground meristem (Fig. 211). divisions are also seen in the protoderm (Figs. 210, 211).  Periclinal The upper  free margins of the lemma do not extend above the expanded lemma apex to form 'ears'.  The point of attachment of the awn to the lemma  is not marked by a constriction.  The awn base is approximately as  wide as the rest of the awn. The absence of a group of smaller cells at the junction of the awn and lemma (Fig. 211) probably accounts for the presistence of the awn.  Callus Initiation and early development of the callus is similar to that of 0. virescens, 0. hymenoides and 0. micrantha.  In a l l four species  67  periclinal divisions i n the ground meristem at the base of the lemma indicate the beginning of the callus (Figs. 212, 213).  Also, the  ground meristem forms the bulk of the tissue of the callus.  In the  early stages of growth the young callus does not have the hemispherical shape that i s so characteristic of the callus of 0. virescens and 0. micrantha.  Instead, at the time of initiation of the posterior  portion of the gynoecial wall, the callus has a downward-directed, broadly acute apex, similar in shape to that of 0. hymenoides (Fig. 215) . The calluses in 0. hymenoides show some Interesting  differences  in their development. In 0. hymenoides elongation of ground meristem cells downward and obliquely outward is responsible for the pointed shape of the callus (Fig. 119).  The protodermal cells at the tip  of the callus remain small (Fig. 119).  In 0. kingii ground meristem  cells in the distal and central portions of the callus on the anterior side expand longitudinally downward, parallel with the adjacent protoderm (Fig. 216).  The sharps point of the callus is mainly the  result of oblique expansion of the protodermal cells at the t i p , i n a direction outward and away from the floret axis (Fig. 216). Two other developmental features are of interest. is attached to the rachilla there  Where the callus  are regular c e l l files (Fig. 217),  described as tabloid cells by Maze et a l . (1971) for Stipa t o r t i l i s . On the posterior side of the rachilla adjoining the base of the floret there i s a projection  (Figs. 204, 218).  This projection differs from  a similar one in 0. micrantha in that i t is formed primarily by the  68  anticlinal elongation of ground meristem c e l l s .  Palea The palea in 0. kingii develops in the same manner as in the other three species (Figs. 219, 220, 221).  At maturity, i t has a narrow  base and a rather long biseriate distal portion (Fig. 222).  Stamens The anther 'beards' are of protodermal origin.  Elongation of the  protodermal cells begins when the anterior portion of the gynoecial wall is initiated.  Lodicules Initiation and growth of the lodicules is as in the other three species.  In 0. kingii the lodicules are smaller. Development of the  posterior lodicule i s shown in Figures 220, 221, and 222.  Stages in  the growth of the anterior lodicules are seen in Figures 223 and 224.  Gynoecium This structure is similar to the gynoecia of the other three species.  However, the initiating divisions appear on the posterior  side of the floret apex at a lower l e v e l , leaving a more distinct residual apex (Fig. 226).  When the posterior side of the gynoecial  wall begins to grow upward, the residual apex develops directly into the ovule (Fig. 227).  As in the other species, the lateral sides of  69  the gynoecial wall develop as the styles (Figs. 228, 229). The styles are situated a short distance apart from each other (Fig. 231), as ^  9.' virescens. At anthesis, the ovarian cavity is 'closed' by the  proliferation of tissues on the inner margins of the ovary wall (Figs. 230, 230a).  Ovule and embryo sac development Integuments Both the inner and outer integuments are f i r s t seen on the upper side (Figs. 232, 233, 234). The archesporial c e l l is distinguished early in integument development (Fig. 232). This was also noticed in 0. hymenoides. There is only one bump in the chalazal region of the outer integument. Nucellus Growth of the nucellus is as in the other three species. There are not as many periclinal divisions in the nucellar protoderm as there are in 0. virescens. Embryo sac A hypodermal c e l l functions as the megaspore mother c e l l (Fig. 234). The megaspores are commonly arranged in a linear tetrad (Fig. 235). The chalazal megaspore i s the functional one (Fig. 236). Stages in megagametogenesis are seen in Figures 237, 238, 239 and 240.  Figure  238 shows a frequently encountered situation in which the abortion of the three non-functional megaspores is delayed until the 2-nucleate embryo sac stage.  70  The embryo sac before the differentiation of the egg and the synergids is spindle-shaped (Fig. 240).  The micropylar and chalazal  ends broaden out later in growth (Fig. 241).  Visible signs of  differentiation in each of the synergids are the development of small, scattered vacuoles and a filiform apparatus (Fig. 241).  The egg  becomes highly vacuolate (Figs. 240a, 241a). The polar nuclei fuse before f e r t i l i z a t i o n .  Fertilization The pollen tube seems to discharge i t s contents into one of the synergids.  Inall the florets examined the two synergids degenerate  prior to f e r t i l i z a t i o n . integrates completely.  In some florets one of the synergids disRemnants of the pollen tube contents are seen  in the persistent degenerate synergid (Figs. 242, 242a, 242b). In other florets, both the degenerate synergids persist, though one of them becomes appreciably smaller. Figure 243 shows the f i r s t zygotic division of the fertilized egg.  Chromatin-like bodies are seen in  the larger, degenerate synergid.  Post-fertilization The outer integument is s t i l l prominent at the 2-cell embryo stage (Figs. 244, 244b). The endosperm is nuclear i n i t i a l l y . antipodals form a considerable mass at this stage.  The  The synergids are  s t i l l visible after the f i r s t zygotic division (Figs. 244a, 244b).  71  Oryzopsis asperifolia Michx. Floret organogenesis This species lacks a posterior lodicule. floret appendages follows this sequence: anterior lodicules, gynoecium and callus. Figures 245, 246, 247 and 248.  The initiation of the  lemma, palea and stamens, This is i l l i s t r a t e d in  The slow rate of development of the  lemma, with respect to the rest of the floret, is unique here. At the time initiating divisions of the gynoecium form on the posterior side of the floret apex (Fig. 248), the lemma leaves the stamens and the gynoecium exposed.  Up t i l l the time of the 4-nucleate stage in embryo  sac development, the lemma does not overtop the stamens and styles, but leaves half their length exposed (Figs. 249, 250, 251).  Only at  the 8-nucleate embryo sac stage does thelemma extend above the rest of the floret.  Awn-lemma The awn-lemma primordium is the f i r s t structure to develop from the floret apical meristem (Fig. 245). The floret apex is striking in i t s large size.  Like the other four species, the floret apex has a one-  layered tunica and undergoes displacement and re-orientation i n the course of floret development.  Figures 247 and 252 show the awn-lemma  primordium of a floret at the time of gynoecium i n i t i a t i o n .  The cells  in the distal portion are larger and more vacuolate than the cells in the lower portion of the primordium.  This distal portion is the future  awn, and i t elongates rapidly (Fig. 248). When the posterior portion  1  72  of the gynoecial wall i s initiated, the awn-lemma junction is barely perceptible, and the lemma is more or less equally wide i n sagittal section (Fig. 253). Ground meristem cells on both the adaxial and abaxial sides of the lemma apex start to divide periclinally.  Just  before the inception of the integuments in ovule development, the lemma apex becomes expanded, (Fig. 254), a result of the previously mentioned periclinal divisions plus some c e l l enlargement. There are fewer periclinal divisions in the abaxial ground meristem than there are in the adaxial ground meristem. At the same time, some adaxial protodermal cells have divided periclinally once. At this stage the awn base is marked out from the lemma apex by a constriction, as a result of fewer c e l l divisions.  The expanded  portion of the lemma is spread over almost half the total length of the lemma (Figs. 249, 250, 254, 255). The convex adaxial side of the lemma apex is mainly the result of c e l l division i n the ground meristem, forming a tissue of considerable size (Fig. 256). Just before the megaspore mother c e l l undergoes meiosis, the patterns of c e l l division on this side of the lemma apex are obliterated, as a result of c e l l expansion i n a horizontal plane (Fig. 256). At the same time, on the abaxial side of the lemma apex, the ground meristem cells expand, parallel with the adjacent protoderm, and the growth patterns due to periclinal divisions are s t i l l obvious. The abaxial ground meristem cells at the lemma apex form a narrow strip of tissue in sagittal section as compared with the adaxial ground meristem (Fig. 256). Later, greater c e l l expansion in the abaxial ground meristem produces  73  a tissue as wide as the adaxial ground meristem (Fig. 257).  Callus Like the awn-lemma, the callus i s initiated at a later stage i n floret development in comparison with the other four species of Oryzopsis that have been described.  This structure is not obvious  until the gynoecial wall has appeared on the posterior side of the floral apex (Figs. 258, 259). Initiation and growth of the callus i s mainly through cell division in the ground meristem (Figs. 258, 259, 260, 261, 263). Early in its development the callus on the anterior side forms a rounded protuberance (Fig. 260). Some protoderm cells on the same side divide periclinally once (Figs. 259, 260, 261, 263). Continued c e l l divisions in the ground meristem increase the size of the rounded callus (Fig. 261). In a mature floret, the callus forms an open ring around the base of the floret, with the edges meeting on the median posterior side (Fig. 154). In off-set sections parallel with the sagittal plane, the posterior callus can be seen as a slight bulge, the result of periclinal divisions i n the protoderm and the ground meristem (Figs. 262, 265). Figures 261 and 262 are of a floret at the stage when integument formation has been completed i n ovule development. The i n i t i a l l y rounded hump of the callus begins to be directed slightly downward at the megaspore mother c e l l stage i n ovule development (Fig. 263). Some of the protodermal cells i n the upper part of the callus elongate to form hairs.  The protodermal cells at  the base of the callus divide once or twice to form a small patch of  74  multiple protoderm (Fig. 263).  Further distension downward produces  an obtusely-angled callus tip (Fig. 264).  The massive callus is mainly  the result of the large number of cells rather than cell expansion. The basal patch of multiple protoderm on the anterior side i s no longer recognisable at maturity.  On the posterior side, the callus i s also  distended downward slightly, and a multiple protoderm is seen clearly in the rounded tip (Fig. 265). For ease of comparison, a table i s presented (TABLE II) of comparable stages i n awn-lemma and callus development i n the five species of Oryzopsis studied, using the stage of gynoecium development as the reference.  TABLE I I . Reference table for comparison of stages in awn-lemma and callus development i n 0. virescens, 0. hymenoides, 0. micrantha,, 0. k i n g i i , and 0. asperifolia, using the stage of gynoecium development as a marker. The numbers refer to figures at the pertinent stages. 0. kingii awnlemma callus  0. asperifolia awnlemma callus  development Initiation of lodicules  19  19  106  113  none none  none  none  252  258  Initiation of anterior gynoecial wall  20  26  107  114  158  168  206  213  252  258  Growth of anterior gynoecial wall  21  27  108  115  163  none  207  214  none  none  Gynoecial wall appears on posterior side of floret apex  22  28  109  116  164  169  208  215  253  259  Ring-shaped gynoecial wall  23  none  110  117  165  170  209  none  none  none  Prior to integument initiation  24  29  none none  none none  none  none  254  260  Initiation of inner integument on upper side  none  none  111  118  166  171  210  216  none  none  Complete inner integument  25  30  none  none  167  172  211  217  255  261 &  Ovule i n orthotropous position  none  none  112  119  none none  none  218  256  263  Stage of gynoecium  0. hymenoides awnlemma callus  0. micrantha awnlemma callus  0. virescens awnlemma callus  76  Palea Growth of the palea is similar to that in the other four species except that in 0. asperifolia c e l l division ceases at a comparatively later stage (Figs. 266, 267, 268, 269).  Stamens The stamens develop in the same manner as in the other species. They are hirsute-tipped at maturity.  Periclinal divisions of the  antherprotoderm occur at the time the anterior portion of the gynoecial wall Initiates (Fig. 266).  The hairs are elongate protodermal hairs.  i Lodicules Only the anterior lodicules are present in this species.  Their  initiation and growth is the same as in the other four species (Figs. 270, 271).  At maturity they are distinctly two-nerved (Fig. 272).  Gynoecium Development of the gynoecium is illustrated in Figures 266, 273, 274, 275, 276 and 277.  The process is very much like that described  in the other four species of Oryzopsis. 279).  There are two styles (Fig.  At anthesis, the ovarian locule is 'closed' by the adpression  of the inner margins of the ovary wall (Figs. 278, 278a).  77  Ovule and embryo sac development Integuments Both the inner and outer integuments initiate on the upper side f i r s t (Figs. 280, 281).  The outer integument has two bumps in the  chalazal region (Figs. 282, 283). Nucellus and embryo sac development Stages in nucellus and embryo sac development are shown in Figures 284, 285 and 286.  Like the other species of Oryzopsis development  of the embryo sac is also of the monosporic 8-nucleate type.  Fertilization and post-fertilization At f e r t i l i z a t i o n only one synergid was seen. The pollen tube seems to enter the embryo sac via the persistent synergid, from which dense, chromatin-like bodies appear to be extruded (Fig. 287). At the 2-cell proembryo stage, remnants of pollen tubes could s t i l l be seen. Where the pollen tube had entered the synergid, a denselystaining material was deposited (Figs. 288a, b).  DISCUSSION  Floret development The sequence of organ initiation in the floret of the five species of Oryzopsis studied differs only in the time of initiation of the callus.  In 0. virescens, 0. micrantha and 0. asperifolia the sequence  of organogeny in the floret i s : (1) lemma; (2) palea and stamens almost  78  simultaneously; (3) lodicules; and (4) gynoecium and callus almost at the same time.  In 0. hymenoides and 0. kingii the callus is precocious  and appears before the gynoecium initiates.  In those species of Stipa  that have been studied developmentally, the callus also appears before the gynoecium initiates.  Growth of the callus in 0. virescens, 0.  hymenoides, 0. micrantha and 0. kingii is primarily due to c e l l enlargement.  In 0. asperifolia the conspicuous collar-like callus  is mainly the result of c e l l division. With the exception of the callus, the young stages of the developing florets prior to gynoecium development are remarkably similar in the five species of Oryzopsis studied.  Comparable stages in species of  Stipa and Oryzopsis studied by Maze et a l . (1971, 1972), also bear a striking resemblance to those species of Oryzopsis studied by the author. Developmental differences that are diagnostic for the species begin to appear when the gynoecial wall i s initiated on the posterior side of the floret apex. The probable basis for the similarity of the early stages in floret development is this:  The mature form of an  organism is the result of developmental processes. Genes produce effects on the visible morphological characters of the mature organism only through their influence on development. Similarly, mutations directly alter developmental processes, and only indirectly characters. Mutations which act relatively late in ontogeny are less likely to disorganise the whole process of development, with consequential deleterious effects, than those which alter the earlier stages (Stebbins, 1950). The mutations established, therefore, w i l l be  79  those that affect development at the latest stage for the modification of the mature structure.  That part of the ontogeny which is not  affected by the mutations w i l l exhibit similarity. As a rule, embryological characters are constant within a genus, (Cave, 1953). Oryzopsis is no exception.  Inter-relationships of 0. virescens, 0. hymenoides, 0. micrantha, 0. k i n g i i , 0. asperifolia, 0. miliacea, S. lemmoni, S. hendersoni, S. t o r t i l i s , and S. richardsoni. Table III presents characters derived from developmental features in 6 species of Oryzopsis and 4 species of Stipa.  Since the taxonomic  problem presented by Oryzopsis involves not only the nature of the inter-relationships between i t s species but also i t s intricate relationship with Stipa, a comparison of Oryzopsis and Stipa species rather than a comparison of Oryzopsis species alone is more meaningful. Data on 0. virescens, 0. hymenoides, 0. micrantha, 0. kingii and 0. asperifolia are from the author's own studies; data on 0. miliacea, S_. lemmoni, S_. hendersoni and S. t o r t i l i s are from a publication of Maze et a l . (1972) .  In this paper by Maze et a l . the data on S_.  hendersoni were taken from Mehlenbacher (1970) and modified by them. Data on S. richardsoni are also from Maze, but unpublished.  Some of  the characters analyzed are similar to those analyzed by Maze et a l . (1972), but the author has deleted some of the characters in the afore-mentioned publication, and has added some new ones. For each measurable character, only one measurement was taken.  The author is  80  f u l l y aware that there i s no provision f o r a range of v a r i a t i o n f o r each measurement.  However, the time-consuming nature of developmental  studies mitigates against multiple measurements. For each character, data f o r a l l ten species were taken and the mean was calculated.  A two-state  coding of characters was used:  those greater than the mean were treated as plus (+); those less than the mean minus (-). The percentage s i m i l a r i t y among species was calculated using the simple matching c o e f f i c i e n t of Sokal and Sneath r'  (1963), S sm  -  n  x 100, '  S where  S m  g m  =  percentage of s i m i l a r i t y ,  =  the number of character matches (positive and negative),  n  =  the number of characters.  The c o e f f i c i e n t s of s i m i l a r i t y obtained are presented  i n the form  of a s i m i l a r i t y matrix i n Table IV. The c o e f f i c i e n t s of s i m i l a r i t y of 0. miliacea and S_. t o r t i l i s , and of 0. micrantha and S_. t o r t i l i s are the lowest.  This i s i n t e r e s t i n g because these two species of  Oryzopsis are considered to be clear-cut Oryzopsis species, and S_. t o r t i l i s i s a ' t y p i c a l l y S t i p o i d ' species.  The other s i m i l a r i t y  c o e f f i c i e n t s seem to f a l l into a pattern of continuous  variation.  81 TABLE I I I . 5*  Comparison o f d e v e l o p m e n t a l f e a t u r e d  P l l l a c c a , Stlp» l e m m o n l l , S. h e n d e r s o n i ! , S.  o f O r y z o p a l a v i r e s c e n s , 0. hymcnotdeg. 0. m i c r a n t h a , 0. k t n f t l l , 0. a s p e r i f o l i a , t o r t i l i s and S. r i c h a r d s o n i 1. 0. vlr.  0. hym.  0. mic.  0. kin.  1. T h i c k n e s s l n number o f c e l l s , o f t h e ground m e r i s t e m o f t h e lemma apex.  19  18  12  8  2. A n g l e o f g r o w t h , i n d e g r e e s , r e l a t i v e t o t h e l o n g i t u d i n a l a x i s o f t h e a v n , i n t h e ground m e r i s t e m on t h e a d a x i a l s i d e o f t h e lemma apex.  88  125  128  3. A n g l e o f g r o w t h , i n d e g r e e s , r e l a t i v e t o t h e l o n g i t u d i n a l a x i s o f t h e a v n , l n t h e ground m e r i s t e m on t h e a b a x i a l s i d e o f t h e lemma apex.  10  56  4. Sclerenchyma mother c e l l s l n awn ground m e r i s t e m .  -  5. Number o f p r o t o d e r m l a y e r s on t h e a d a x i a l s i d e o f t h e lemma apex  0. asp.  0. mil.  S. 1cm*.  S. hen.  S. tor.  S. rlc.  14  6  19  20  21  13  88  91  65  74  85  117  83  22  80  75  68  90  27  66  73  -  -  -  -  -  +  -  +  +  4  1  2  2  2  1  5  6  7  1  71  NA  82  77  88  NA  36  63  95  NA  7. Number o f p r o t o d e r m l a y e r s on t h e a b a x i a l s i d e o f t h e lemma apex.  1  1  1  1  1  1  1  1  2  1  8. Number o f p r o t o d e r m l a y e r s on t h e a d a x i a l s i d e o f t h e awn base.  1  1  1  1  1  1  1  1  5  1  9. Number o f p r o t o d e r m l a y e r s on t h e a b a x i a l s i d e o f t h e awn base.  1  1  1  1  1  1  1  1  2  1  10. R a t i o awn w i d t h a t b a s e / w i d t h o f awn-lemma J u n c t i o n i n s a g g l t a l plane.  1.1  2.2  1.21  0.93  1.1  1.27  0.82  1.23  1.00  0.97  11. R a t i o lemma w i d t h a t a p e x / v i d t h o f awn-lemma j u n c t i o n l n s a g g l t a l plane.  1.8  2.0  2.0  1.2  1.1  1.45  1.39  1.73  1.0  1.08  0.73  1.2  1.5  3.3  1.2  1.33  3.5  3.5  0.63  1.0  24  NA  4  3  6  NA  16  31  47  NA  0.27 -0.04 0.016 0.017  0.30  0.50  Character  6. A n g l e o f g r o w t h , i n d e g r e e s , r e l a t i v e t o t h e l o n g i t u d i n a l a x i s o f t h e a v n , I n t h e m u l t i p l e p r o t o d e r m on t h e a d a x i a l s i d e o f t h e lemma apex.  12. R a t i o , l o n g e s t c e l l ( a n t i c l i n a l p l a n e ) I n protoderm on a d a x i a l 6 l d e o f lemma a p e x / l o n g e s t c e l l ( a n t i c l i n a l p l a n e ) i n p r o t o d e r m on a d a x i a l s i d e o f lemma below apex. 13. T o t a l number o f p r o t o d e r m c e l l s l n m u l t i p l e p r o t o d e r m a t lemma apex. 14. H e i g h t ( i n mm.) o f a p i c a l p o r t i o n o f t h e f r e e m a r g i n o f t h e lemma above t h e awn-lemma j u n c t i o n when t h e magaspore mother c e l l i s horizontal.  0.46  0.08 0.001  0.02  -  -  -  -  -  -  -  +  -  100  57  138  68  127  92  48  66  21  42  0.43  0.19  0.48  0.17  0.65  2.46  0.73  1.25  0.39  0.54  18. T h i c k n e s s l n number o f c e l l s i n t h e ground m e r i s t e m o f t h e c a l l u s along a l i n e p e r p e n d i c u l a r t o the l o n g i t u d i n a l a x i s of the c a l l u s .  6  7  4  4  12  4  9  8  7  6  1 9 . T a b l o i d c e l l s a t t h e attachment o f t h e f l o r e t t o t h e s p l k e l e t .  -  -  -  -  -  +  +  +  +  +  -  +  -  -  +  +  +  -  -  -  -  +  22. P e r i c l i n a l d i v i s i o n s i n c a l l u s p r o t o d e r m .  -  •+  2 1 . Protoderm peg on t h e p o s t e r i o r s i d e o f t h e f l o r e t base.  -  +  -  -  1.8  2.5  2.5  1.4  1.0  2.5  1.7  1.5  0.5  1.1  15  12  8  5  7  4  12  5  4  4  0  3  3  rlO  0  100  -100  -2  -1  -1  42  41  37  40  37  85  30  40  30  42  2  1  1  1  2  2  1  1  1  1  0.59  0.85  0.76  0.83  0.93  0.40  0.84  0.61  0.63  0.67  15. R i d g e i n lemma apex I n f r o n t a l p l a n e . 16. A n g l e , i n d e g r e e s , formed by t h e c a l l u s t i p . 17. R a t i o a r e a o f l a r g e s t p r o t o d e r m c e l l / a r e a o f l a r g e s t ground meristem c e l l i n c a l l u s .  20. Protoderm peg on t h e p o s t e r i o r s i d e o f t h e s p l k e l e t a x i s .  23. R a t i o p a l e a l c n g h t / l e n g t h o f a n t e r i o r g y n o e c i a l w a l l when t h e p o s t e r i o r w a l l o f t h e gynoecium i s i n i t i a t e d . 24. T h i c k n e s s I n number o f c e l l s a t t h e p a l e a base. 25. R e l g h t , l n u , above t h e attachment o f t h e a b a x i a l g y n o e c i a l w a l l , o f the s i t e o f i n i t i a t i o n o f the p o s t e r i o r gynoecial w a l l . 26. A n g l e , i n d e g r e e s , o f d i v e r g e n c e o f t h e o v u l e f r o m t h e l o n g i t u d i n a l a x i s o f t h e f l o r e t when t h e i n t e g u m e n t s a r e i n i t i a t e d . 27. Number o f bumps l n t h e o u t e r Integument.' 28. R a t i o l e n g t h o f t h e o v u l e a t t a c h e m c n t t o t h e p l a c e n t a / l e n g t h the o v u l e c a . f e r t i l i z a t i o n . 29. F i l i f o r m a p p a r a t u s . 30. R a t i o l e n g t h / v l d t h 31. Egg s t a r c h .  embryo s a c c a . f e r t i l i z a t i o n .  of  -  +  +  +  +  +  •+  -  +  +  2.7  1.9  2.2  2.6  1.7  3.0  2.4  2.7  3.6  2.3  -  -  +  • -  +  +  •  -  -  -  TABLE IV. Similarity matrix ( % ) of Oryzopsis virescens, 0. hymenoides, 0. micrantha, 0. k i n g i i , 0. miliacea, Stipa lemmoni, S. hendersoni, S_. t o r t i l i s , and S. richardsoni.  0. virescens  0. 0. 0. hymenoi- micran- kingii tha des  0. asperifolia  0. s. s. s. miliacea henderlemmoni tortilis soni  0. hymenoides  68.96  0. micrantha  53.33  75.00  0- kingii  45.16  55.17  60.00  0. asperifolia  51.61  58.62  66.66  68.75  0. miliacea  55.17  44.82  60.71  51.72  65.51  s. lemmoni  58.06  68.96  50.00  67.74  54.83  34.48  s. hendersoni  58.06  58.62  46.66  54.83  48.38  37.93  s. t o r t i l i s  41.93  51.72  26.66  51.61  45.16  24.13 . 64.51  51.61  s. richardsoni  58.62  55.17  46.42  82.75  68.96  55.17,  55.17  CO  to  61.29  65.51  62.06  83  Inter-relationships of the 10 species were analyzed using a 2-dimensional ordination.  The ordination technique used i s that  used by Bray and Curtis (1957).  This technique, which i s outlined  below, attempts to extract from a matrix of s i m i l a r i t y c o e f f i c i e n t s a s p a t i a l pattern i n which the distance between two species i s d i r e c t l y related to their degree of s i m i l a r i t y .  In other words, a high degree  of s i m i l a r i t y w i l l be represented by a low s p a t i a l separation. In this technique, the inverse of the s i m i l a r i t y c o e f f i c i e n t between two species i s equated with l i n e a r distance.  The inversions  are accomplished by subtracting each c o e f f i c i e n t of s i m i l a r i t y from a maximum s i m i l a r i t y value of 100.  The two species which have the  lowest c o e f f i c i e n t of s i m i l a r i t y ( = the highest inverse c o e f f i c i e n t ) are chosen as the end points of the X-axis.  These two species are  0. miliacea and S_. t o r t i l i s , which are separated by a l i n e a r distance of 75.9  units.  The p o s i t i o n of any species on the X-axis i s calculated  by Beal's equation  (cited by Gauch and Whittaker,  L X  1972):  + D  = 2L  where  X  =  the p o s i t i o n of the species on the X-axis,  L  =  distance between end points of the X-axis, distance of species from the f i r s t end point (= inverse c o e f f i c i e n t of species and miliacea),  0.  84  D  2 =  distance of species from the second end point (= inverse coefficient of species and S. tortilis).  To construct the Y-axis, two new end points are selected which are in close proximity on the X-axis, but which are nevertheless separated by a high degree of dissimilarity.  It is important that the  end points are constructed of species which are most dissimilar, otherwise the axes w i l l not cover the total range of variability expressed by the inverse coefficients.  The results of this ordination  technique are presented i n Figure 289. With regard to i t s correct generic disposition, 0. hymenoides has been somewhat of an enigma. Johnson (1972) comments that i t s affinities are puzzling, because morphologically, (according to Johnson, 1945a), i t resembles 0. virescens in some respects (viz., an indurate lemma and an open panicle), while i t s distribution and hybridization with Stipa suggest some relationship with Stipa. Developmentally the affinities of 0. hymenoides are with Stipa (Fig. 289) . Morphologically, 0. hymenoides has been deemed to be an Oryzopsis on the basis of i t s diffuse panicle, deciduous awn, and indurate lemma. However, these three characters are not unknown i n species of Stipa. An open panicle i s present in S_. richardsoni L., S_. porteri Rydb. (= Ptilagrostis porteri (Rydb) Weber) , S_. lepida Hitchc., S_. cernua Stebbins and Love: S. neomexicana (Thurb.) Scribn., S. webberi (Thurb.)  Y 50 +  0. asperifolia x  x 0. kingii  40-0. micrantha x :( 0. miliacea  S_. richardsoni y S_.: t o r t i l i s  30 -•  X  S_. lemmoni x 20  Oo hymenoides  oo  X X  So hendersoni 10  0. virescens 1  1  10  20  KH  30  1  1  1  1  1  40  50  60  70  80  X  FIG. 289. Ordination results to show inter-relationships of Oryzopsis virescens, 0. hymenoides, 0. micrantha, 0. k i n g i i , 0. asperifolia, 0. miliacea, Stipa lemmoni, S_. hendersoni, S_. t o r t i l i s , and S_. richardsoni.  86  Johnson, and S_. ichu Hara have deciduous awns (see Maze et a l . , 1966); S. viridula Trin., S_. lemmoni (Vasey) Scribn.r," and S_. hendersoni (Vasey) Mehlenbacher have indurate lemmas. On the other hand, 0. hymenoides possesses features that are strongly suggestive of a Stipa, v i z . , a sharp callus, pilose lemma, and involute leaves. Besides the 1 stipoid' morphological features present in 0. hymenoides i t s crossibility with species of Stipa provide further positive evidence of i t s affinity with Stipa.  Hybridization between  0. hymenoides and eleven different species of Stipa have been documented by Weber (1957), Johnson and Rogler (1943), and by Johnson (1945b, 1960, 1962, 1963). A f e r t i l e amphiploid from a cross between 0. hymenoides and S_. viridula was recovered in nature by Nielson and Rogler (1952). Johnson suggests that the chromosome number of n = 24 in 0. hymenoides could indicate i t s origin by amphiploidy between the 12-chromosome line of Stipa and the 12-chromosome line of Oryzopsis. Even so, i t s chromosome number and i t s postulated amphiploid origin do not preclude i t from being a Stipa.  A count of n = 24 in S_.  splendens Trin. was reported by Love and Myers in 1947 (cited by Darlington and Wylie, 1955). Evidence from developmental, morphological and hybridization studies suggest that the affinity of 0. hymenoides is with Stipa. Oryzopsis miliacea and 0. virescens belong to section Piptatherum, which consists of a coherent group of species marked by specialization in characters that distinguish them from Stipa (reduction of callus, induration, dorsiventral flattening and increase in size of the lemma,  87  increase i n length and nervation of the glumes). Morphological studies by Johnson indicate that in this section, 0. virescens forms a closely-knit group with 0. paradoxa, 0. coerulescens and 0. holciformis, while 0. miliacea is set apart from them. The results in this study show that 0. miliacea is closer to 0. micrantha than i t is to 0. virescens. There are no developmental data on other Eurasian species of Oryzopsis for comparison, but i t is not unreasonable to predict a high degree of similarity between 0. virescens, 0. paradoxa, 0. coerulescens and 0. holciformis on the basis of their development. The relationship between 0. miliacea and 0. micrantha w i l l be discussed after a consideration of the section Oryzopsis, to which 0. micrantha belongs. The North American species of 0. micrantha, 0. pungens, 0. exigua, 0. canadensis and 0. kingii  constitute diploidsof the section Oryzopsis  — they form a group marked by specialization in characters (differentiation of the callus; development of a twisted, persistent awn; indurate lemma) which merge with the genus Stipa.  At one end, 0. micrantha  is detached from the other species of the same section by i t s resemblance to 0. miliacea; at the other end 0. kingii intergrades completely with Stipa.  The three species in between reportedly form a gradated  series towards Stipa.  The sectional disposition of 0. micrantha was  questioned by Elias (1942), who placed i t in Piptatherum. On the basis of morphological and developmental data, 0. miliacea should be removed from Piptatherum, and perhaps placed in section Oryzopsis. However, evidence from other sources must be considered  88  before such a re-arrangement is attempted. According to Johnson (1945a, 1972), the Eurasian species of Oryzopsis are diploids with a count of n = 12, and the North American diploids have a count of n = 11.  However, in Oryzopsis and Stipa, i t is d i f f i c u l t to relate  the geographic distribution with chromosome number. In genera in which polyploidy i s rampant, such as Oryzopsis and Stipa, chromosome number loses i t s value as a guide to generic and sectional delimitation (Rollins, 1953). Furthermore, a count of n = 12 in 0. pungens has been reported by Bowden (1960). Besides the five n = 11 diploids in section Oryzopsis, there are two other species, 0. asperifolia (n = 23) and 0. swallenii (n = 17; Hitchcock and Spellenberg, 1968). The latter species i s , like 0. k i n g i i , a borderline species between Oryzopsis and Stipa (Hitchcock and Spellenberg, 1968). Until Mehlenbacher (1970) did a thorough study of S_. hendersoni, (n = 17; Spellenberg, 1968), this species too was placed in the scetion Oryzopsis as Oryzopsis hendersoni (Vasey) . The relationships between 0. micrantha, 0. kingii and 0. asperifolia, and between them and the other seven species, compared developmentally, are expressed in Figure 289.  As they stand, 0.  virescens seems to be isolated from the other nine species, and there does not seem to be a discontinuity between the following nine species: 0. miliacea, 0. micrantha, 0. asperifolia, 0. k i n g i i , S_. richardsoni, 0. hymenoides (Stipa), 0. hendersoni, S_. lemmoni and £5. t o r t i l i s . In this connection, i t is interesting to note that Hoover (1966),  89  considered 0. miliacea (L.) Bentham and Hooker to be Stipa miliacea (L.) Hoover; and to quote Hoover, "the separation of a group of species as the 'genus' Oryzopsis does violence to the relationships of the plants".  CONCLUSION Data from morphology, distribution, and hybridization studies suggest that Oryzopsis hymenoides belongs to the genus Stipa. Developmentally i t also shows a high degree of similarity to Stipa. This further supports the contention that 0. hymenoides be transferred to Stipa. Morphologically, 0. miliacea is set apart from 0. virescens and other members of the section Piptatherum. Developmental studies have upheld morphological data.  It is suggested that 0- miliacea be  removed from Piptatherum. With the removal of 0. miliacea, 0. virescens 0. paradoxa, 0. coerulescens and 0. holciformis would form a more well-defined section.  Further studies on other members in the Oryzopsis  are needed before the inter-relationships between 0. micrantha, 0. asperifolia and 0. kingii can be understood.  It would seem that  more comprehensive studies of the genus Oryzopsis w i l l either lead to i t s mergence with Stipa or at least to a redefinition of the sections of Oryzopsis.  90  LITERATURE CITED  Arber, A. 1925. Monocotyledons: a morphological study. Botanical Handbooks. Cambridge.  Cambridge  1926. Studies in the Gramineae. I. The flowers of certain Bambuseae. Ann. Bot. 40: 447-469. 1927. Studies in the Gramineae. I I . Abnormalities i n Cephalostachyum virgatum Kurz, and their bearing on the interpretation of the bamboo flower. Ann. Bot. 41: 47-74.  i  1928. Studies in the Gramineael IV. I. The sterile spikelets of Cynosurus and Lamarkia. 2. Stamen-lodicules in Schizostachyum. 3. The terminal leaf of Gigantochloa. Ann. Bot. 42: 173-187. 1934. The Gramineae: a study of cereal, bamboo and grass. Cambridge Univ. Press. London. Barnard, C. 1955. Histogenesis of the inflorescence and flower of Triticum aestivum L. Australian J . Bot. 3: 1-20. 1957a. Floral histogenesis in the monocotyledons. Gramineae. Australian J . Bot. 5: 1-20.  I. The  1957b. Floral histogenesis in the monocotyledons. I I . The Cyperaceae. Australian J . Bot. 5: 115-128. 1958. Floral histogenesis in the monocotyledons. I I I . Juncaceae. Australian J . Bot. 6: 185-198. •  The  1960. Floral histogenesis in the monocotyledons. IV. The Liliaceae. Australian J . Bot. 8: 213-225.  Bews, J.W. 1929. The World's Grasses. Their differentiation, distribution, economics and ecology. Longmans, Green and Co., London. Boke, N.H. 1947. Development of the adult shoot apex and floral initiation in Vinca rosea L. Amer. J . Bot. 34: 433-439. ________ 1949. Development of the stamens and carpels in Vinca rosea L. Amer. J . Bot. 36: 535-547. Bonnett, O.T. 1953. Developmental morphology of the vegetative and f l o r a l shoots of maize. Univ. I l l i n o i s , Agr. Exp. Sta. Bull. 568.  91  1961. The oat plant: its histology and development. Univ. I l l i n o i s , Agr. Exp. Sta. Bull. 672. Bowden, W.M. 1960. Chromosome numbers and taxonomic notes on northern grasses. III. Twenty-five genera. Can. J . Bot. 38: 541-577. ... Bray, J.R. and J.T. Curtis. 1957. An ordination of the upland forest communities of southern Wisconsin. Ecol. Monogr. 27: 325-349. Brooks, R.M. 1940. Comparative histogenesis of vegetative and floral apices in Amygdalus communis with special references to the carpel. Hilgardia 13: 249-306. Brown, W.V. 1949. A cytological study of cleistogamous Stipa leucotricha. Madrono 10 (3): 65-96. Buder, J . 1928. Der Bau des phanerogamen.Vegetationspunktes und seine Bedeutung fiir die Chimarentheorie. Ber. deutsch. bot. Ges. 46: 20-21. Cannon, W.A. 1900. A morphological study of the flower and embryo of the wild oat, Avena fatua L. California Acad. S c i . , Proc. 3 (Botany) 1: 329-364. Cave, M.S. 1953. Cytology and embryology in the delimitation of genera. Chronica Botanica, 14 (3): 140-153. Cheung, M. and R. Sattler. 1967. Early floral development of Lythrum salicaria. Can. J . Bot. 45: 1609-1618. Corner, E.J.H. 1946. 27: 423-437.  Centrifugal stamens.  J . Arnold Arboretum,  Cronquist, A. 1968. The evolution and classification of flowering plants. Houghton M i f f l i n , Boston. Darlington, CD. and A.P. Wylie. plants. London.  1953.  Chromosome atlas of flowering  Davis, G.L. 1966. Systematic embryology of the Angiosperms. John Wiley and Sons, Inc., New York, London, Sydney. Davis, P.H. and V.H. Heywood. 1965. Principles of Angiosperm taxonomy. Oliver and Boyd, Edinburgh and London. D i b o l l , A.G. 1968. Fine structure development of the megagametophyte of Zea mays following f e r t i l i z a t i o n . Amer. J . Bot. 55: 787-806.  92  Eckardt, T. 1957. Vergleichende Studien iiber die Morphologischen Beziehungen zwischen Fruchblatt, Samenanlage und Blutenachse bei einigen Angiospermen. Neue Hefte zur Morphologie, 3: 1-91. Weimar. E l i a s , M.K. 1942. Tertiary Prairie grasses and other herbs from the high plains. Geol. Soc. of America special papers 41: 1-176. Fagerlind, F. 1958. Is the gynoecium of the Angiosperms built up in accordance with the phyllosporous or the stachyosporous scheme? Svensk Bot. Tidskr. 52: 421-425. Feder, N. and T.P. O'Brien. 1968. Plant microtechnique: some principles and new methods. Amer. J . Bot. 55: 123-142. Gauch, H.G. and R.H. Whittaker. 1972. Comparison of ordination techniques. Ecology. 53: 868-875. Gould, F.W.  1968.  Grass systematics. McGraw-Hill, New York.  Guttenberg, H.V. 1960. Grundziige der Histogenese hoheren Pflanzen. I. Die Angiospermen. Handbuch der Pflanzenanatomie. 2e Aufl. ed. Zimmerman-Ozenda. Band VIII, Teil 3. Berlin-Nikolassee. Hackel, E. 1881. Untersuchungen iiber die Lodiculae der Graser. Bot. Jahrb. 1: 336-361. 1889. Gramineae. In Engler and Prantl, Die Naturlichen Pflanzenfamilien, II. 2: 1-97. Hitchock, A.S. 2nd ed.  1951. Manual of the grasses of the United States. U.S. Dep. Agr. Misc. Publ. 200.  Hitchcock, C.L. and R. Spellenberg. 1968. Idaho. Brittonia 20: 162-165.  A new Oryzopsis from  Hitchcock, C.L., A. Cronquist, M. Ownbey, and J.W. Thompson. 1969. Vascular plants of the Pacific North-West, I. University of Washington Press, Seattle and London. Holt, I.V. 1954. Initiation and development of the inflorescences of Phalaris arundinacea L. and Dactylis glomerata L. Iowa State C o l l . J . S c i . 28: 603-621. Hoover, R.F. 1966. Miscellaneous new names for California plants. Leaflets of Western Botany, 10 (16): 337-350. Jensen, W.A. and D.B. Fisher. 1968. Cotton embryogenesis: The entrance and discharge of the pollen tube in the embryo sac. Planta 78: 158-183.  93  Johansen, D.A.  1940. Plant microtechnique.  McGraw-Hill, New York.  Johnson, B.L. 1945a. Cytotaxonomic studies in Oryzopsis. 107: 1-31.  Bot. Gaz.  1945b. Natural hybrids between Oryzopsis hymenoides and several species of Stipa. Amer. J . Bot. 32: 599-608. 1960. Natural hybrids between Oryzopsis and Stipa. I. Oryzopsis hymenoides x Stipa speciosa. Amer. J . Bot. 47: 736-742. 1962. Natural hybrids between Oryzopsis and Stipa. II. Oryzopsis hymenoides x Stipa nevadensis. Amer. J . Bot. 49: 540-546. 1963. Natural hybrids between Oryzopsis and Stipa. III. Oryzopsis hymenoides x Stipa pinetorum. Amer. J . Bot. 50: 228-234. 1972. Polyploidy as a factor in the evolution and distribution of grasses. In The biology and utilization of grasses, ed. V.B. Younger and C.M. McKell (a volume of Physiological Ecology). Academic Press, New York and London. Johnson, B.L. and G.A. Rogler. 1943. A cyto-taxonomic study of an intergeneric hybrid between Oryzopsis hymenoides and Stipa viridula. Amer. J . Bot. 30: 49-56. Kadry, A.E.R. 1946. Embryology of Cardiospermum halicacabum L. Svensk Bot. Tidskr. '40: 111-126. Kaplan, D.R. 1968. Histogenesis of the androecium and gynoecium in Downihgia bacigalupii. Amer. J . Bot. 55: 933-950. Kaufman, P.B. 1959. Development of the shoot of Oryza sativa L. II. Leaf histogenesis. Phytomorphology 9: 277-311. Kaussman, B. 1941. Verleichende Untersuchungen iiber die Blattnatur der Kelch-, Blumen- und Staub- Blatter. Bot. Arch.. 42: 503-572. Klaus, H. 1966. Ontogenetische und histogenetische Untersuchungen an der Gerst (Hordeum distichon L.) Bot. Jahrb. 85: 45-79. Maheshwari, P. 1950. An introduction to the embryology of Angiosperms. McGraw-Hill Book Co., Inc., New York, Toronto and London. 1961. Embryology in relation to taxonomy. In Recent advances in botany, IX th International Botanical Congress, Montreal, 1959. 2 vol. Univ. of Toronto Press, pp 679-682.  94  Maze, J . and L.R. Bohm. 1973. Comparative embryology of Stipa elmeri (Gramineae). Can. J . Bot. 51: 235-247. Maze, J . , N.G. Dengler, W.R. Hildreth, and R. Myatt. 1966. The reduced awns of some members of the genus Stipa and their possible relationship to dispersal mechanisms. Amer. J . Bot. 53: 632. Maze, J . , L.R. Bohm, and L.E. Mehlenbacher, J r . 1970. Embryo sac and early ovule development in Oryzopsis miliacea and Stipa t o r t i l i s . Can. J . Bot. 48: 27-41. Maze, J . , N.G. Dengler, and L.R. Bohm. 1971. Comparative floret development in Stipa t o r t i l i s and Oryzopsis miliacea (Gramineae). Bot. Gaz. 132: 273-298. Maze, J . , L.R. Bohm, and C.E. B e i l . 1972. Studies on the relationships and evolution of supraspecific taxa u t i l i z i n g developmental data. I. Stipa lemmoni (Gramineae). Can. J . Bot. 50: 2327-2352. McCoy, R.W. 1940. Floral organogenesis i n Frasera carolinensis. Amer. J . Bot. 27: 600-609. Mehlenbacher, L.E. 1970. Floret development, embryology, and systematic position of Oryzopsis hendersoni (Gramineae). Can. J . Bot. 48: 1741-1759. Merxmuller, H. and P. Leins. 1967. Die Verwandtschaftsbeziehungen der Kreuzblutler und Mohngewachse. Bot. Jahrb. 86: 113-129. Michaux, A.  1803. Flora Boreali- Americana  Vol. 1. Paris,  p. 51.  Mohamed, A.H., and F.W. Gould. 1966. Biosystematic studies in the Bouteloua curtipendula complex. I I . Megasporogenesis and embryo sac development. Amer. J . Bot. 53: 166-169. Moeliono, B.M. 1970. Cauline or carpellary placentation among the dicotyledons. Koninklijke van Gorcum, N.V. Assen. Nielson, E.L., and G.A. Rogler. 1952. An amphiploid of x Stiporyzops i s . Amer. J . Bot. 39: 343-348. Pankow, H. 1959. Histogenetische Untersuchungen an der Plazenta der Primllaceen. Ber. deutsch. bot. Ges. 72: 111-122. 1962. Histogenetische Studien an der Blviten einiger Phanerogamen. Bot. Stud. Heft. 13: 1-106. Pankow, H. and H.V. Guttenberg. 1959. Studien uber die Anlage der Achselknospen und Blattprimordien bei Graminnen. Planta 52: 629-643.  95  Philipson, W.R. 1935. The development of the spikelet in Agrostis canina L. New Phytol. 34: 421-436. 1934.  The morphology of the lemma. New Phytol. 33:  Pilger, R.  1954.  Das System der Gramineae. Bot. Jahrb.  Pohl, R.W.  1968.  How to know the grasses. W.C.  76:  359-371. 281-384.  Brown Co., Iowa.  Rohweder, 0. 1963. Anatomische und histogenetische Untersuchungem an Laubsproszen und Bluten der Commelinaceen. Bot. Jahrb. 82: 1-99. Rollins, R.C. 1953. Cytogenetical approaches to the study of genera. Chronica Botanica 14: 133-139. Roth, I. 1959. Histogenese und Morphologische Deutung der Plazenta von Primula. Flora 148: 129-152. Rowlee, W.W. 1898. The morphological significance of the lodicules of grasses. Bot. Gat. 25: 199-203. Rudiger, W. 1939. Die Sproszvegtationspunkte Beitr. B i o l . Pflanz. 26: 401-443.  einiger Monocotylen.  Satina, S. and A.F. Blakeslee. 1943. Periclinal chimeras in Datura in relation to the development of the carpel. Amer. J . Bet. 30: 453-462. Sattler, R. 1966. Towards a more adequate approach to comparative morphology. Phytomorphology 16: 417-429. _________ 1967. Petal inception and problem of pattern detection. J . Theoretical Bat. 17: 31-39. Schultze-Motel, W. 1959. Entwicklungsgeschichtliche und vergleichendmorphologische Untersuchungen im Bliitenbereich der Cyperaceae. Bot. Jahrb. 78: 129-170. Schuster, J . 1910. Ueber die Morphologie der Grasbliite Flora 100: 213-266. Sharman, B.C. 1943. Tannic acid and iron alum with safranin and orange G in studies of the shoot apex. Stain Technol. 18: 105-111. 106:  1945. Leaf and bud initiation in the Gramineae. Bot. Gat. 269-289.  96  1960a. Development of the inflorescence and spikelets of Anthoxanthum odoratum L. New Phytol. 59: 60-64. 1960b. Developmental anatomy of the stamen and carpel primordia in Anthoxanthum odoratum L. Bot. Gaz. 121: 192-198. Shechter, Y. and B.L. Johnson. 1968. The probable origin of Oryzopsis contracta. Amer. J . Bot. 55: 611-618. Singh, V. and R. Sattler. 1972. Floral development of Alisma t r i v i a l e . Can. J . Bot. 50: 619-627. Sokal, R.R. and P.H.A. Sneath. 1963. Principles of numerical taxonomy. W.H. Freeman, San Francisco. Soma, K. 1958. Morphogenesis in the shoot apex of Euphorbia lathyris. J. Fac. S c i . Tokyo Univ. Sect. III. Bot. 7: 199-256. Spellenberg, R.W.. 1968. Notes on Oryzopsis hendersoni (Gramineae). Madrono, 19: 283-286. Spellenberg, R.W. and L.E. Mehlenbacher. 1971. Anatomical and cytological studies of an intergeneric hybrid, Oryzopsis hendersoni x Stipa lemmoni (Gramineae). Can. J . Bot. 49: 1565-1574. Sprotte, V.K. 1940. Fruchbliitter.  Untersuchungen liber Wachstum und Nervatur der Bot. Arch. 40: 463-506.  Stebbins, G.L. 1950. Univ. Press.  Variation and evolution in plants. Columbia  _________ 1956. Cytogenetics and evolution of the grass family. Amer. J . Bot. 43: 890-905. 1972. The evolution of the grass family. In The biology and utilization of grasses, ed. Younger, V.B. and CM. McKell. (a volume of Physiological Ecology). Academic Press, New York, London. Tepfer, S.A. 1953. Floral anatomy and ontogeny in Aquilegia formosa var. truncata and Ranunculus repens. Univ. California Pub. Bot. 25: 513-648. Thompson, J.M. 1937. On the place of ontogeny in floral enquiry. Publ. Hart. Bot. Lab. 17: 3-20. T r o l l , W. 1939. Die morphologische Natur der Karpelle. Botanica 5: 38-41.  Chronica  97  True, R.H. 18:  1893. On the development of the caryopsis. 212-226.  Bot. Gaz.  Tucker, S.C. 1959. Ontogeny of the inflorescence and the flower in Drimys winteri var. chilensis. Univ. California Pub. Bot. 30: 257-336. Tucker, S.C. and E.M. Gifford. 1966a. Organogenesis in the carpellate flower of Drimys lanceolata. Amer. J . Bot. 53: 433-442. 1966b. Carpek development in Drimys lanceolata. J . Bot. 53: 671-678.  Amer.  Verzar-Petri, G. and G. Baranyai-Szentpetery. 1960. Beitrage zur Entwicklungsgeschichte des Gynazeums von Datura stramonium L. Acta Biol. Ac. S c i . Hung. 11: 155-174. Weatherwax, P. 1942. Morphology of the spikelet of Oryzopsis hymen hymenoides. Amer. J . Bot. 29 (Suppl): 195. Weber, W.A. 1957. A new intergeneric natural hybrid involving Oryzopsis and Stipa (Gramineae). Rhodora 59: 273-277. Weier, C E . and H.M. Dale. 1960. A development study of wild r i c e , Zizania aquatica. Can. J . Bot. 38: 719-739. Wylie, R.B. 1941. Some aspects of fertilization in Vallisneria. Amer, J . Bot. 28: 169-174.  98  APPENDIX  For ease of reference, the figures which are from the same floret are grouped together:  0. virescens (Trin.) Beck. 8, 15; 9, 18, 31, 51; 10, 19, 32, 40; 11, 20, 26, 33, 57; 12, 21, 27, 34, 41, 58; 13, 24, 29, 56, 67, 68, 80; 22, 28, 35, 42, 62, 63, 207; 25, 36a,b,c, 38, 44; 30, 37, 43, 81; 39, 48, 55; 46, 52; 47, 54; 60, 61; 64, 65, 66, 79; 69, 70, 71, 72; 73, 82.  j). hymenoides (Roem. & Schult.) Ricker 101, 106, 113, 120;  99  APPENDIX (continued)  102, 107, 114, 121; 103, 109, 116, 122, 125, 131; 104, 110, 117, 132; 108, 115, 130; 111, 118, 123, 123a, 124, 126, 129; 127, 128.  0. micrantha (Trin. & Rupr.) Thurb. 158, 159, 168; 160, 164, 169, 177, 181; 161, 165, 170, 175, 178, 182; 163, 174; 166, 171, 183; 167, 172; 176, 180,  0. kingii (Boland.) Beal. 199, 205, 212, 219; 200, 206, 213, 220; 201, 215, 221, 223; 202, 209, 227, 228; 203, 210, 216, 222, 224, 229; 207, 214;  101  FIGS. 1 - 6 .  Floral parts.  f i g . 1, spikelet;  Figs. 1, 2, 3, Oryzopsis virescens;  f i g . 2, floret side view;  view. Figs. 4, 5, 6, 0. hymenoides; side view; a, awn;  f i g . 3, floret posterior  f i g . 4, spikelet; f i g . 5, floret  f i g . 6, floret posterior view. Line represents ltnm.;  c, callus;  e, ears at apex of lemma; 1, lemma; p, palea.  100  APPENDIX (continued)  208, 226; 204, 218; 211, 217.  asperifolia Michx. 247, 252, 258, 266; 248, 253, 259, 267, 270; 249, 254, 260, 268, 271; 251, 257; 255, 261, 262; 256, 263, 269; 264, 265; 273, 274.  102  1D*> FIGS. 8 - 14. Stages In floret development in 0. virescens. Fig. 8, awn-lemma initiation (unlabeled arrow). Fig. 9, palea and stamen initiation.  Fig. 10, lodicule i n i t i a t i o n .  Fig. 11, gynoecium  initiation.  Fig. 12, spikelet during growth of anterior portion of  gynoecial wall (unlabeled arrow shows awn-lemma junct on). floret prior to integument i n i t i a t i o n .  Fig. 13,  Fig. 13 a, b, c, cross-sections  of floret at levels shown i n f i g . 13. Fig. 14, floret at megaspore mother c e l l stage. gynoecial wall; p, palea;  Lines represent 0.05 mm.;  a l , anterior lodicule;  p i , posterior lodicule;  a, awn;  c, callus;  s, stamen.  ag, anterior  1, lemma;  104  FIGS. 15 - 20. Stages i n floret development in 0. virescens. awn-lemma initiation (unlabeled arrow).  Fig. 15,  Fig. 16, early awn-lemma  growth. Fig. 16a, young spikelet at approximately the same stage as f i g . 16. Fig. 17, awn-lemma at later stage. initiation.  F i g . 19, lodicule i n i t i a t i o n .  gynoecium. Lines represent 0.01 mm.; wall;  agl, anterior glume;  1, lemma; p, palea; posterior lodicule;  Fig. 18, palea and stamen Fig. 20, initiation of  a, awn; ag, anterior gynoecial  a l , anterior lodicule;  pc, procambium; s, stamen;  c, callus;  pgl, posterior glume; p i ,  t - , outer tunica layer.  106  no,  FIGS. 21 - 25. Stages in awn-lemma development in 0. virescens. Lines represent 0.01 mm.;  unlabeled arrows indicate junction between  awn and lemma; e, ears at apex of lemma; pc, procambium; v t , vascular tissue.  s, stamen;  108  109  FIGS. 26 - 30. Stages in callus development in 0. virescens. Lines represent 0.01 mm.; pc, procambium.  unlabeled arrows indicate axils of lemma;  110  FIGS. 31 - 39.  Stages i n f l o r e t development i n 0. virescens.  31, 32, palea i n i t i a t i o n and early growth. i n i t i a t i o n and developing palea.  F i g . 33, posterior l o d i c u l e  F i g , 34, young flower and palea.  Fig. 35, young flower and palea at i n i t i a t i o n of posterior wall.  F i g . 36, palea and posterior l o d i c u l e .  lodicule.  lodicule;  p, palea;  a l l other l i n e s  ag, anterior gynoecial w a l l ; pc, procambium;  p i , posterior l o d i c u l e ;  Figs. 37, 38,  F i g . 39, cross-section of posterior  Line i n f i g . 36 represents 0.05 mm.,  represent 0.01 mm.;  gynoecial  F i g . 36 a, b, c,  portions of palea at l e v e l s indicated i n f i g . 36. developing posterior l o d i c u l e .  Figs.  s, stamen.  a l , anterior  pg, posterior gynoecial  wall;  112  113. FIGS. 40 -56.  Stages in stamen and anterior lodicule development in  0. virescens.  Figs. 40 - 44, anterior lodicule. Figs. 4 5 - 4 9 ,  cross-sections of anterior lodicule; lodicules (unlabeled arrows);  f i g . 45, initiation of anterior  f i g . 46, spread of initiation in  posterior direction (unlabeled arrow); with distinct posterior margin; margins distinct;  f i g . 47, anterior lodicule  f i g . 48, posterior and anterior  f i g . 49, mature anterior lodicule. Fig. 50, whole  structure of anterior lodicules, adaxial view. Fig. 51, stamen initiation (unlabeled arrow). Figs. 52 - 55, cross-sections of stamens, stippling indicates sporogenous c e l l s . stamen, tangential section.  Fig. 56, lateral  Line in f i g . 50 represents 0.1  a l l other lines represent 0.01 mm.;  circle in f i g s . 46 - 49  represents anterior axis of floret;  a l , anterior lodicule;  anterior margin;  pc, procambium;  pm, posterior margin.  mm.,  am,  114  FIGS. 57 - 72. Stages in gynoecium development in 0. virescens. Fig. 57, initiation of anterior gynoecial wall. of anterior gynoecial wall.  Fig. 58, early growth  Fig. 59, frontal section of young gynoecium  Figs. 60, 61, cross-sections of young gynoecium, 14 ja apart; f i g . 61 is at a higher level than f i g . 60. Figs 62, 63, adjacent sections 14 ju apart.  Figs. 64, 65, 66, adjacent serial sections 14 M apart,  showing a distinct posterior gynoecial wall ('querzone'), and the beginning of style branches. Figs. 69, 70, 71, 72, serial crosssections of young gynoecium, 14 ju. apart, and of increasing height from left to right. Lines represent 0.01 mm.; wall;  ag, anterior gynoecial  fm, floret apical meristem; l g , lateral gynoecial wall;  pg, posterior gynoecial wall; branch.  p i , posterior lodicule;  sb, style  116  >I7  FIGS. 73 - 77.  Stages in gynoecium development in 0. virescens.  Fig. 73, style branch with developing stigmatic hairs (unlabeled arrows).  Figs. 74, 74a show the same cross-section;  Figs. 75, 75a are from the same cross-section; f i g . 75a, ovary; of the floret.  f i g . 74a, floret.  f i g . 75, 'stylar core';  circle in both figs, represents the anterior axis Fig. 76, ovary and anterior lodicules, abaxial view.  Fig. 77, a series of transverse sections from the base upwards of a young floret at the megaspore stage;  the sections are 14 ja apart.  Lines in figs. 74a, 75a, 76 represent 0.1 mm., 0.01 mm.; trace;  agt, anterior gynoecial trace; c l , cleft;  gynoecial trace; region;  a l l other lines represent  a l t , anterior lodicule  l g t , lateral gynoecial trace; s, style;  s t , stamen;  sh, stigmatic hair;  s t t , stamen trace.  pgt, posterior s r , stylar core  Stippling shows procambium.  118  119  FIGS.  78 - 84.  Early stages i n ovule and embryo sac development i n  0. virescens.  Figs. 78, 79, development of posterior portion of  gynoecial wall  (unlabeled  cytoplasmic c e l l s .  s t i p p l i n g indicates densely  F i g . 80, young gynoecium.  of inner integument. integument.  arrows);  F i g . 81, i n i t i a t i o n  Figs. 82, 82a, same section* i n i t i a t i o n of outer  Figs. 83, 83a, same section, megaspore mother c e l l stage.  Fig. 84, meiosis I I . Lines i n f i g s . 82a, 83a represent 0.05 mm.; a l l other l i n e s represent 0.01 mm.; growth patterns; meristem;  agt, anterior gynoecial  i i , inner integument;  outer integument;  double-headed arrows indicate trace;  fm, f l o r e t a p i c a l  mme, megaspore mother c e l l ; o i ,  ov, ovule trace (= posterior gynoecial  trace).  120  FIGS. 85 - 90. Stages i n ovule and embryo sac development i n 0. virescens.  F i g s . 85, 85a, megaspore stage, from the same s e c t i o n ;  f i g . 85, ovule;  f i g . 85a, gynoecium.  F i g . 86, development of second  bump i n outer integument at megaspore stage.  F i g . 87, T-shaped t e t r a d ,  w i t h one degenerated megaspore ( i n d i c a t e d by arrow and s o l i d b l a c k ) . F i g s . 88, 88a, same section at f u n c t i o n a l megaspore stage; ovule;  f i g . 88a, whole gynoecium.  F i g . 89, 2-nucleate stage.  90, 90a, same s e c t i o n at 4-nucleate stage; whole gynoecium.  integument;  Figs.  f i g . 90, ovule; 90a,  Lines i n f i g s . 85a, 88a, 90a represent 0.05 mm.,  a l l other l i n e s represent 0.01 mm.; growth patterns;  f i g . 88,  b^, f i r s t bump;  o i , outer integument.  double-headed arrows i n d i c a t e b^, second bump;  i i , inner  122  FIGS. 91 - 98.  Stages i n embryo sac development i n 0. virescens.  Figs. 91, 91a, same section at 8-nucleate stage; f i g . 91a, whole gynoecium. 8-nucleate stage;  f i g . 91, ovule;  Figs 92, 93, same section at d i f f e r e n t i a t e d  f i g . 92, embryo sac;  f i g . 93, egg and synergids.  Figs. 94, 95, same embryo sac p r i o r to f e r t i l i z a t i o n ; embryo sac;  f i g . 95, egg and synergids.  at f e r t i l i z a t i o n ; and integuments;  Figs. 96, 97, same section  f i g . 96, egg apparatus and surrounding nucellus f i g . 97, ovule.  and nuclear endosperm.  F i g . 98, embryo sac with proembryo  Line i n f i g . 91a represents 0.05  other l i n e s represent 0.01 mm.; indicate growth patterns;  pe, proembryo.  mm.,  all  double-headed arrows i n f i g . 91  c, chromatin-like bodies;  homogenous dense staining material; integument;  f i g . 94,  e, egg;  i i , inner integument;  h,  o i , outer  124  FIGS. 99 - 105. Stages in floret development in 0. hymenoides. F i g . 99, lemma initiation (unlabeled arrow). (unlabeled arrow).  Fig. 100, palea initiation  Figs 101 - 105, outline diagrams of entire florets;  f i g . 101, at lodicule initiation (unlabeled arrow indicates site of posterior lodicule initiation);  f i g . 102, at initiation of anterior  portion of gynoecial wall (unlabeled arrow);  f i g . 103, at initiation  of posterior portion of gynoecial wall (unlabeled arrow); prior to integument initiation;  f i g . 104,  f i g . 105, megaspore mother c e l l stage.  Lines in f i g s . 99, 100 represent 0.01 mm., a l l other lines represent 0. 05 mm.;  a, awn;  1, lemma; p, palea.  a l j , awn-lemma junction; c, callus;  g l , glume;  1X1  FIGS. 106 - 1 1 2 . S t a g e s i n awn-lemma development i n 0. hymenoides. L i n e s r e p r e s e n t 0.01 mm.; lemma;  p c , procambium;  arrows i n d i c a t e j u n c t i o n between awn and s , stamen.  128  /49  FIGS. 113 - 119. Stages in callus development in 0. hymenoides. Lines represent 0.01 mm.; agl, anterior glume;  unlabeled arrows indicate axils of lemma;  pgl, posterior glume.  IZI  FIGS. 120 - 128. Stages in floret development in 0. hymenoides. Figs. 120, 121, flower and palea. palea.  Fig. 122, posterior lodicule and  Fig. 123, posterior lodicule and palea.  Fig. 123a, t i p of  palea shown in f i g . 123. Fig 124, posterior lodicule. Figs. 125, 126, development of anterior lodicule. Fig. 127, whole structure of anterior lodicules, adaxial view. Fig. 128, same lodicules as f i g . 127, but abaxial veiw and with ovary attached. Line in f i g . 123a represents 0.05 mm., lines in figs. 127 and 128 represent 1.0 mm., a l l other lines represent 0.01 mm.; wall;  p, palea;  pc, procambium;  ag, anterior portion of gynoecial p i , posterior lodicule;  s, stamen.  132  FIGS. 129 - 134.  Stages i n f l o r e t development i n 0. hymenoides.  Fig. 129, portion of stamen, anther 'beard' i n i t i a t i o n . growth of anterior portion of gynoecial w a l l .  F i g . 131, gynoecial  wall appears on posterior side (unlabeled arrow). gynoecium.  F i g . 130,  F i g . 132, young  F i g . 133, cross-section of top of ovary to show s t y l a r core  t i s s u e , heavy l i n e (arrow) indicates 'closure' of locule. cross-section of gynoecium;  f i g s . 133 and 133a are of the same section,  c i r c l e i n both indicates anterior axis of f l o r e t . structure of ovary. 134,  0.05 mm.,  of gynoecial w a l l .  F i g . 134, whole  Line i n f i g . 133a represents  a l l other l i n e s represent  of gynoecial wall;  F i g . 133a,  0.1 mm.,  0.01 mm.;  fm, f l o r e t a p i c a l meristem;  in fig.  ag, anterior portion  pg, posterior portion  134  FIGS. 135 - 140. hymenoides.  Ovule and early embryo sac development i n 0. hymenoide  Figs. 135, 135a, same section at inner integument i n i t i a t i o  i n i t i a t i o n on upper side (unlabeled arrow i n f i g . 135); f i g . 135, ovule;  f i g . 135a, gynoecium.  F i g . 136, ovule at i n i t i a t i o n of  outer integument on upper side (unlabeled arrow).  Figs. 137, 137a,  same section at i n i t i a t i o n of outer integument on lower side (unlabeled arrow);  f i g . 137, ovule;  f i g . 137a, gynoecium.  same section at megaspore mother c e l l stage;  Figs. 138, 138a,  f i g . 138, ovule; f i g .  138a, gynoecium.  Figs 139, 139a, same section at megaspore stage;  f i g . 139, ovule;  f i g . 139a, gynoecium.  F i g . 140, functional megaspore.  Lines i n f i g s . 135a, 137a, 138a, 139a represent 0.05 mm., l i n e s represent 0.01 mm.; patterns; ii,  a l l other  double-headed arrows indicate growth  s o l i d black i n f i g . 140 represents aborted megaspores;  inner integument;  o i , inner integument.  136  t$7  FIGS. 141 - 143.  Stages i n embryo sac development i n 0. hymenoides.  Fig. 141, 4-nucleate stage. sac at 8-nucleate stage;  F i g s . 142, 142a, from same same embryo  f i g . 142, ovule;  f i g . 142a, egg.  Figs.  143, 143a, 143b, from same embryo sac p r i o r to f e r t i l i z a t i o n ; f i g . 143, embryo sac;  f i g . 143a, egg and one synergid;  Lines represent 0.01 mm.; f i l i f o r m apparatus; o i , outer integument; sy, synergid.  f i g . 143b, ovule.  dsy, degenerating synergid;  i i , inner integument; p, polar nucleus;  e, egg; f a ,  nv, nucleolar vacuole;  psy, persistent synergid;  138  /39 FIGS. 144 - 146. i n 0. hymenoides.  F e r t i l i z a t i o n and early p o s t - f e r t i l i z a t i o n  F i g . 144, adjacent s e r i a l section, 7 ju. apart, of  egg apparatus at f e r t i l i z a t i o n ; nucellus and inner integument; f i g s . 144c, 144d,  stages  f i g . 144a, f i g . 144b,  two synergids.  egg and  surrounding  egg and two  synergids;  F i g . 145, adjacent s e r i a l sections,  7 ju apart, of egg apparatus at f e r t i l i z a t i o n ;  f i g . 145a,  egg, degenerat  degenerate synergid and surrounding nucellus and integuments; 145b,  145c,  egg and synergids.  Lines represent 0.01  mm.;  dense s t a i n i n g material; psy, persistent synergid; bodies;  F i g . 146, 2 - c e l l proembryo stage.  dsy, degenerate synergid; ii,  s?, sperm n u c l e i ? .  figs.  inner integument;  pt, p o l l e n tube;  h, homogenous  o i , outer integument;  sn, chromatin-like  140  f  FIGS. 147 - 154. micrantha;  F l o r a l parts.  f i g . 147, s p i k e l e t ;  149, f l o r e t posterior view. spikelet;  Figs 147, 148, 149, Oryzopsis f i g . 148, f l o r e t side view; f i g .  Figs. 150, 151, 0. k i n g i i ;  f i g . 151, f l o r e t side view.  asperifolia;  f i g . 152, spikelet;  154, lemma posterior view. the same magnification;  Figs. 152, 153, 154, 0.  f i g . 153, lemma side view; f i g .  Line represent  a, awn;  f i g . 150,  1.0 mm.,  c, c a l l u s ;  a l l drawings at  1, lemma;  p, palea.  142  FIGS. 155 - 162.  Stages in floret development in 0. micrantha. F i g .  155, awn-lemma initiation (unlabeled arrow).  Fig. 156, early awn-  lemma growth. Fig. 157, Initiation of posterior lodicule (unlabeled arrow).  Fig. 158, initiation of anterior portion of gynoecial wall.  Fig. 159, spikelet same section as f i g . 158. F i g . 160, spikelet at initiation of posterior gynoecial wall (unlabeled arrow). floret prior to integument i n i t i a t i o n .  Fig. 161,  Fig. 162, floret at megaspore  mother c e l l stage. Lines in figs. 159, 160, 161, 162,represent 0.05 mm., a l l other lines represent 0.01 mm.; lodicule; palea;  c, callus;  g, glume;  a, awn;  a l , anterior  1, lemma; pc, procambium; p,  p i , posterior lodicule; s, stamen.  144  FIGS. 163 - 167. Stages in awn-lemma development in 0. micrantha. Lines represent 0.01 mm.; v t , vascular tissue.  e, ears;  pc, procambium;  s, stamen;  146  141  FIGS. 168 - 173. Stages in callus development in 0. micrantha. Unlabeled arrows indicate axils of lemma; lines represent 0.01 v t , vascular tissue.  mm.;  148  FIGS. 174  - 18.5.  Figs. 174,  175,  Stages i n f l o r e t development i n 0. micrantha. palea and posterior l o d i c u l e .  anterior l o d i c u l e . adaxial view. 182, 184a,  183,  F i g . 179,  Figs. 180,  181,  Figs. 176  -  178,  anterior l o d i c u l e s , whole structures, development of gynoecial w a l l .  l a t e r stages i n gynoecial w a l l development.  same section of top of ovary;  f i g . 184,  Figs.  ovary;  F i g . 185,  ovary and anterior l o d i c u l e s , abaxial view.  Line i n f i g .  l i n e s i n f i g s . 179 and 185 represent  a l l other l i n e s represent 0.01  wall;  fm, f l o r e t a p i c a l meristem;  wall;  p i , posterior l o d i c u l e ;  region.  fig.  c i r c l e i n both diagrams indicates anterior axis of f l o r e t .  184 represents 0.1 mm., mm.,  184,  'stylar core' region,  heavy black l i n e (arrow) indicates adpressed inner margins; 184a,  Figs.  mm.;  ag, anterior  p, palea;  gynoecial  pg, posterior  sb, s t y l e branch;  0.5  gynoecial  s r , ' s t y l a r core'  150  1*1 FIGS. 186 - 191.  Ovule and embryo sac development in 0. micrantha.  Fig. 186, inner integument on upper and lower side. integument see on upper side. Fig. 189, megaspore stage. surrounding nucellus. 0.01 mm.;  Fig. 187, outer  Fig. 188, megaspore mother c e l l stage.  Fig. 190, 2-nucleate embryo sac and  Fig. 191, 4-nucleate.  A l l lines represent  i i , inner integument; mme, megaspore mother c e l l ; o i ,  outer integument.  152  /5"3  FIGS. 192 - 196. Stages in embryo sac development in 0. micrantha. Fig. 192, 8-nucleate stage, before differentiation of egg and synergids. Fig. 193, 8-nucleate stage with differentiated egg and synergids. Fig. 193a, egg from same embryo sac as F i g . 193. Fig. 194, egg apparatus, polar nuclei about to fuse, surrounding nucellus and integuments prior to f e r t i l i z a t i o n . Fig. 195, post-fertilization.  Fig. 195a, fertilized (?) egg and synergids;  Figs. 195 and 195a are from the same embryo sac. Fig. 196, 2-cell proembryo stage.  A l l lines represent 0.01 mm.; e, egg; es, starch granules  in egg; pt, pollen tube; sn, chromatin-like bodies.  154  FIGS. 197 - 2Q4. Stages in floret development in 0. k i n g i i . F i g . 197, spikelet at early avm-lemma growth (unlabeled arrow). spikelet at palea and stamen i n i t i a t i o n . diagrams of whole florets;  Fig. 198,  Figs. 199 - 204, outline  f i g . 199, early growth of lodicules;  f i g . 200, at initiation of anterior gynoecial wall (unlabeled arrow); f i g . 201, at initiation of posterior portion of gynoecial wall (unlabeled arrow);  f i g . 202, prior to integument initiation; f i g .  203, at inner integument i n i t i a t i o n , unlabeled arrow indicates awnlemma junction;  f i g . 204, megaspore mother c e l l stage.  Lines i n  f i g s . 197, 198 represent 0.01 mm., a l l other lines represent 0.05 mm.;  a, awn;  a l , anterior lodicule;  lemma; p, palea; initiation;  c, callus;  p i , posterior lodicule;  sz, site of stamen i n i t i a t i o n .  g l , glume;  pz, site of palea  1,  156  157FIGS. 205 - 211. Stages in awn-lemma development in 0. k i n g i i . Lines represent 0.01 mm.;  unlabeled arrows indicate junction between  awn and lemma; pc, procambium;  s t , stamen;  v t , vascular tissue.  158 I  FIGS. 212 - 218.  Stages in callus development in 0. k i n g i i .  212 - 217.are drawings of calluses,  Figs.  f i g . 218 is a drawing of the  posterior side of the rachilla immediately below the attachment of the floret.  Lines represent 0.01 mm.;  axils of lemma; t , tabloid cells;  unlabeled arrows Indicate  v t , vascular tissue.  FIGS. 219 - 231. Stages in floret development in 0. k i n g i i . F i g . 219, young flower and palea.  Fig. 220, young flower and palea at  initiation of anterior gynoecial wall (unlabeled arrow). 222, posterior lodicule and palea.  Figs. 221,  Figs. 223, 224, anterior lodicule;  unlabeled arrow In f i g . 223 indicates axil of anterior stamen. 227, 228 are adjacent serial sections; gynoecial wall;  Figs.  f i g . 227, growth of posterior  f i g . 228, arrow indicates growth of lateral portion  of gynoecial wall into a style branch.  Fig. 229, young gynoecium.  Figs. 230, 230a show the same cross-section;  f i g . 230, 'stylar core'  region at top of ovary, heavy line (indicated by unmarked arrow) shows 'closure' of ovarian locule;  f i g . 230a, ovary;  both f i g s , represent anterior axis of floret.  circle i n  Fig. 231, anterior  lodicules and ovary, abaxial view. Line i n f i g . 230a represents 0.1 mm.;  in f i g . 231, 0.05 mm.;  a l , anterior lodicule; p, palea; s, stamen;  a l l other lines represent 0.01 mm.;  fm, floret apical meristem; i , integument;  pg, posterior gynoecial wall; sb, style branch;  p i , posterior lodicule;  s r , 'stylar core' region.  162 S  FIGS. 232 - 239.  Ovule and early embryo sac development in 0. k i n g i i .  Fig. 232, inner integument initiation on upper side (unlabeled arrow). Fig 233, inner integument initiation on lower side. integument on both upper and lower sides.  Fig. 234, outer  F i g . 235, megaspore stage.  Fig. 236, functional megaspore, solid black indicates aborted megaspores.  Fig. 237, 2-nucleate.  F i g . 238, 2-nucleate stage with 3  persistent megaspores, embryo sac outlined with heavy black l i n e . Fig. 239, 4-nucleate. o i , outer, integument;  Lines represent 0.01 mm.;  i i , inner integument;  pm, persistent megaspores.  164  I (,6  FIGS. 240  - 244.  F i g . 240, ovule. f i g . 240.  Stages i n embryo sac development i n 0. k i n g i i . F i g . 240a, egg, from the same embryo sac shown i n  F i g . 241, embryo sac with fused polar n u c l e i .  egg, from same embryo sac shown i n f i g . 241.  Figs. 242,  adjacent s e r i a l sections 7 jn apart, at f e r t i l i z a t i o n ; embryo sac;  f i g s . 242a, 242b, egg, one synergid, and  nucellus and inner integument;  heavy l i n e  e, egg;  f a , f i l i f o r m apparatus;-  nucleolar vacuole;  ii,  o i , outer integument;  n u c l e a r - l i k e material;  f i g . 242, surrounding  F i g . 243, zygotic  Figs. 244, 244a, 244b, adjacent  sections 7 ;u apart at 2 - c e l l proembryo stage. mm.;  242a, 242b,  (arrow) indicates boundary  between n u c e l l a r protoderm and inner integument. d i v i s i o n and two synergids.  F i g . 241a,  sy, synergid;  serial  Lines indicate 0.01  inner integument; pt, pollen tube;  v, vacuole.  nv, sn,  166  FIGS. 245 - 251.  Stages in floret development i n 0. asperifolia.  Fig. 245, awn-lemma initiation (unlabeled arrow). and stamen i n i t i a t i o n . florets;  Figs. 247 - 251, outline drawings of entire  f i g . 247, at initiation of anterior gynoecial wall and  anterior lodicule;  f i g . 248, at initiation of posterior gynoecial  wall,,unlabeled arrow indicates awn-lemma junction; to integument initiation;  wall;  f i g . 251, 4-nucleate  Lines i n figs. 245, 246 represent 0.01 mm.,  represent 0.05 mm.;  a l l other lines  a, awn; agz, initiation site of anterior gynoecial  a l z , site of anterior lodicule initiation;  lemma; p, palea;  f i g . 249, prior  f i g . 250, at megaspore mother c e l l stage,  unlabeled arrow indicates awn-lemma junction; stage.  Fig. 246, palea  c, callus;  1,  pgz, initiation site of posterior gynoecial wall;  pz, site of palea initiation;  sz, site of stamen i n i t i a t i o n .  168  U>9 FIGS. 252 - 257. Stages in awn-lemma development i n 0. asperifolia. Lines represent 0.01 mm.; and lemma; pc, procambium;  unlabeled arrows mark junction of awn s, stamen; v t , vascular tissue.  170  ni FIGS. 258 - 265. Stages in callus development i n 0. asperifolia. Figs. 262 and 265 are the posterior sides of the callus shown i n f i g s . 261 and 264 respectively. arrows denote axils of lemma.  Lines represent 0.01 mm.;  unlabeled  /7S FIGS. 266 - 279.  Stages in floret development in 0. asperifolia.  Fig. 266, flower and palea at initiation of anterior gynoecial wall (unlabeled arrow).  Figs. 267, 268, 269, palea development. Figs.  270, 271, anterior lodicule development. Fig 272, anterior lodicules, whole structures, abaxial view. Fgis. 273, 274, adjacent serial sections of young gynoecium. Fig. 275, frontal section of young gynoecium.  Fig. 276, initiation of posterior gynoecial wall (unlabeled  arrow). Fig. 277, growth of posterior gynoecial wall. 278a, same cross-section of top of ovary;  Figs. 278,  f i g . 278, 'stylar core'  region, contact of inner margins indicated by heavy line (arrow); f i g . 278a, ovary; floret.  circle in both f i g s , indicates anterior axis of  Fig. 279, ovary. Line f i g . 278a represents 0.1 mm., lines  in f i g s . 272, 279 represent 0.5 mm., a l l other lines represent 0.01 mm.;  ag, anterior gynoecial wall;  f l o r a l apex;  a l , anterior lodicule;  l g , lateral gynoecial wall;  gynoecial wall;  s, stamen;  p, palea;  fm,  pg, posterior  s r , 'stylar core' region.  174  ^278  17$  FIGS. 280 - 284. asperifolia. ovule;  Ovule and early embryo sac development in 0.  Figs. 280, 280a are of the same section;  f i g . 280,  f i g . 280a, gynoecium. Fig. 281, megaspore mother c e l l stage.  Fig. 282, megaspore stage.  Fig. 283, functional megaspore;  black indicates aborted megaspores.  solid  Fig 284, 2-nucleate stage.  Line i n f i g . 280a represents 0.05 mm., a l l other lines represent 0.01 mm.;  b^, f i r s t bump; b^i second bump;  o i , outer integument.  i i , inner integument;  176  177  FIGS. 285 - 288.  Stages in embryo sac development and f e r t i l i z a t i o n  in 0. asperiflolia.  Fig. 285, 8-nucleate stage.  from the same embryo sac as f i g . 285.  Fig. 285a, egg,  Figs. 286, 286a, 286b, 8-  nucleate stage, prior to f e r t i l i z a t i o n , a l l from the same embryo sac; f i g . 286, ovule;  f i g . 286a, embryo sac;  egg at f e r t i l i z a t i o n .  f i g . 286b, egg.  Fig. 287,  Figs. 288, 288a, 288b, 2-cell proembryo stage,  from the same embryo sac;  f i g . 288, ovule;  figs. 288a, 288b, 2-cell  proembryo, synergid and surrounding nucellus and integuments. Line in f i g . 288 represents 0.05 mm., an, antipodals; e, egg;  a l l other lines represent 0.01  es, starch granules in egg;  dense staining material; i i , inner integument; pe, proembryo; synergid.  pt, pollen tube;  mm.;  h, homogenous  o i , outer integument;  sn, nuclear-like material;  sy,  178  FIG. 290. Scanning electronmicrograph of young florets of Oryzopsis virescens, during early growth of the awn-lemma. 260 x.  FIG. 291. Scanning electronmicrograph of young florets of 0. virescens, prior to initiation of the gynoecium. 125 x.  Abbreviations for both figures: apical meristem;  a, awn;  g l 1 , f i r s t glume;  a l , awn-lemma;  g l _ , second glume;  f a , floret 1, lemma.  180  FIG. 292. Scanning electronmicrograph of young florets of Oryzopsis virescens, during growth of the anterior portion of the gynoecial wall.  260 x.  Abbreviations:  a, awn;  as, anterior stamen;  ag, anterior portion of gynoecial wall;  1, lemma; p, palea;  p i , posterior lodicule.  182  FIG. 293. Sagittal section of part of a young floret of Oryzopsis virescens, during growth of the anterior portion of the gynoecial wall.  440 x.  Abbreviations: apex;  p, palea;  ag, anterior portion of gynoecial wall; p i , posterior lodicule.  f a , floret  184  FIG. 294. Transverse section at top of ovary in Oryzopsis hymenoides at anthesis.  225 x.  FIG. 295. Frontal longitudinal section of ovary of 0. hymenoides at anthesis.  65 x.  Abbreviations for both figures: stigmatoid tissue;  sc, 'stylar core1 region; s r ,  vb, vascular bundle.  186  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0101004/manifest

Comment

Related Items