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Floret development and embryology of Oryzopsis hendersoni (Gramineae) Mehlenbacher, Lyle Eugene 1970

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FLORET DEVELOPMENT AND EMBRYOLOGY OF ORYZOPSIS HENDERSONI (GRAMINEAE) by Lyle Eugene Kehlenbacber BoS« University of Michigan, Ann Arbor, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of BOTANY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1970 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree tha permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver 8, Canada i Abstract Previous research has shorn, that Orysopsis hendersoni shares two features with Stipa and one with Oryzopsiso A study of floret development and embryology was undertaken in order to obtain more points for comparisono Most of the twenty-six features of 0„ hendersoni resulting from this study are characteristic of Stipa and not Oryzopsisa Therefore, i t is proposed that 0. hendersoni b® transferred to Stipa 0 Evidence from this and other studies demonstrates that grass locidules can be foliar, stamen-like, or intermediate and that the gynoecium is unicarpellate. These facts are contradicted by claims > of homology based on hypothetical phylogenieso Because use of the concept of homology has led to general acceptance of misleading assumptions in these and other instances and because the concept of homology is ambiguous and superfluous, i t should not be usedo i i TABLE OF CONTENTS PAGE INTRODUCTION ' 1 TABLE I 2 MATERIAL AND METHODS . 4 LEAVES AND STEMS 5 LEMMA 6 AWN - - 6 CALLUS 6 PALEA 7 LODICULES 7 STAMENS ' ' 8 GYNOECIUM J 8 INTEGTOffiNTS 9 NUCELLUS 10 EMBRYO SAC ' 10 DISCUSSION OP HOMOLOGY 13 TAXONOMIC CONCLUSIONS 16 TABLE II 17 TABLE III 18 BIBLIOGRAPHY 19 i i i LIST OP TABLES Table I. Summary of Previous Research. II. Summary and comparison of Resultsc Early floret development. III. Summary and Comparison of Results: Embryology. iv LIST OP FIGURES Figs. 1-8. Leaf and stem initiation and early development. Fig. 1. Leaf initiation ° 2-4. Early leaf development. 5» Initiation of branch of inflorescence. v~ 6-8. Early growth of branch of inflorescence. Figs. 9-18. General floret morphology. Fig. 9 . Young floret. 10. Young floret. 11. Young floret. 12. Young floret. 1 12a. Cross section of young floret as shown in Fig. 12. 13. Young floret 14. Young floret. 15. Mature floret. 15a. Cross section of mature floret as shown in Fig. 15. 15b-d Cross section of lemma of mature floret as shown in Fig. 15* 16-18. Mature floret. Figs. 19-26. Lemma and palea initiation and early development. Fig. 19. Lemma initiation. 20-22fi> Early lemma development. V Fig, 23. Palea initiation. Ventral side on right. 24-26. Early palea development. Ventral side on right. Figs. 27-33* Differentiation of awn base, lemma apex, and callus. Fig. 27. Lemma before differentiation. 28. Initiation of differentiation of awn base and lemma apex. 29. Differentiation of awn base and lemma apex 30. Further differentiation of lemma apex. 31. Initiation of callus. 32-33. Callus development. Figs. 34-42. Lodicule initiation and development. Fig. 34. Ventral lodicule initiation. Ventral side on right. 35-37. Early ventral lodicule development. Ventral side on right. 38. Dorsal lodicule initiation. 39-42 Early dorsal lodicule development. Figs. 43-52. Stamen initiation and development. Fig. 43• Stamen initiation. 44-46. Early stamen development. 47-49* Early stamen development. Tangential section. 50-52. Anther wall formation and development of nucleolar vacuoles. vi Pigs. 53-59* Carpel' initiation and early development* Integument and archesporia initiation* F i g o 53• Carpel initiation on dorsal side* 54» Early carpel development on dorsal side. 55• Carpel initiation on ventral side.. Early carpel development on dorsal side, 56. Early oarpel development on dorsal and ventral sides. 57* Series of divisions pushing ovule into lateral position. Integument initiation. ArcheBporial cells. 58"59« Archesporial cells. • , ' Figs. 60-67. Megasporogenesis. F i g . 66-63. Early megasporogenesis. 64-67. Late megasporogenesis. Figs. 68-74* Megagametogenesis. Fig. 68. Early megagametogenesis. 69-74* Late legagametogenesis Figs. 75-78* Late megagametogenesis and fertilization. Fig. 75* Late megagametogenesis. 76. Immediate post-fertilization. " 77-78* Late post-fertilization. 79* Young florets Ventral side on right. 80. Young florets. 81. Carpel .fusion tissue. 82. Starch-filled carpel and dead, pointed outer integument. 83-84. Vacuolated nucleolus of polar nucleus before fusion. 85. Vacuolated nucleolus of polar fusion nucleus. 86. Vacuolated nucleolus of dividing early endosperm. 1 Introduction A grass population was discovered on Clements Mountain, Washington in 1892 by Henderson. VaBey (1893) claimed that i t represented a distinct part of the range of variation in the genus Oryzopsis and named i t Oryzopsis  hendersoni. In 1945? Johnson (1945) published a cytotaxonpmio study on Oryzopsis. He described in detail the three subgenera of Oryzopsis — Piptatherum, Euoryzopsis, and Briocoma — and included 0. hendersoni in Euoryzopsis. Spellenberg (1966) claimed that 0. hendersoni shared certain featurws with section Piptatherum (several-nerved glumes;glabrous, indurate lemma) and some with Stipa (three lodicules, differentiated callus, convolute lemma). These features, together with others reported in Johason (1945a. b, 1962, 1963), A.S. Hitchcock (1950), CL. Hitchcock et al (1969), and Komarow (1934)» are listed in Table I. It can be seen that some species of Stipa have several-nerved glumes and indurate lemmas, and that some species of Oryzopsis have convolute lemmas and many have three lodicules. The only features of 0. hendersoni, considered up to now, that are character-ist i c of any single genus are the pubescent awn and chromosome number shared with Stipa and the glabrous lemma shared with Oryzopsis sect. Piptatherum. Spellenberg (personal communication) has also confirmed that 0. hendersoni forms viable but sterile hybrids with Stipa lemmoni (2N=34) in the field. Because of the uncertainties about the true relationships of 0. hendersoni» a detailed study of floret development and embryology was undertaken. It was hoped that the stages in development of the floral parts and embryo sac would provide more points of comparison between 0__ hendersoni and the other species of Oryzopsis and Stipa. Table I. Summary of Previous Research* Character sect. Piptatherum (p) sect. Eriocoma (Er) sect. Euorysopsis(Eu) Panicle Glumess shape no. nerves f i r s t second Lemmas shape no. nerves summit indurate convolute pubescence Awnt Persitence geniculation texture length Calluss pubescence length. Paleas shape noo nerves No. Lodicules Epiblast Throat of Sheath Style Branch open acute-acuminate 3-9 3-9 elliptic-obovate 3-5 unlobed-lobes yes no glabrous-sparse deciduous-tardy straight-curved scaberulous 3-20mm glabrous-bearded .2mm elliptic 2 small-large glabrous-pubescent reflexed open ovate 3 3-5 broad fusiform 3-5 lobed-long lobed yes no' dense deciduous straight scaberulous 4-8 mm bearded .2mm ellip t i c 2 narrow-open obtuse-acute small-large glabrous-pubescent glabrous erect 1-3 1-3 fusiform 5 unlobed-lobed yes yes sparse-dense deciduous-persistent s traight-geniculate scaberulous 1-12mm glabrous-bearded • 2-.39Bn elliptic 2 2 or 3 small-large Chromosome No. 2N 24,46 28,48 22,46,48 3 Table I. (cont) Affinities of Character Stipa (s) Oo hendersoni 0. hendersoni Panicle narrow-open narrow-open Eu, S Glumest shape no. nerves f i r s t second Lemmas shape no. nerves summit indurate ; convolute pubescence Awn Persistence geniculation texture length Callust pubescence length Paleat shape no. nerves No. Lodicules Epiblast acute-acuminate 3-5 3-7 acute 5-7 3-5 broad fusiform-fusiform broad fusiform lobed-long lobed no-yes yes sparse-dense deciduous-persistent curved-geniculate glabrous-pubescent 5-35IMTI glabrous-bearded .2-7°Omm elliptic 2 3 large Throat of Sheath glabrous-pubescent Style Branch reflexed-erect Chromosome No. 2N 24,32,34,36,44, 46,66,68 ,82 5 lobed yes yes glabrous deciduous curved pubescent 6-1Omm glabrous .3mm elliptic 2 3 large glabrous reflexed 34 P, Eu, S P, S P, Er, Eu, S Er, S P, Er, Eu, S P, Er, Eu, S P, Er, Eu, S Eu, S P P, Er, Eu, S P, Eu, S S P, Er, Eu, S P, Eu, S Eu, S P, Er, Eu, S P, Er, Eu, S P, Er, Eu, S P, Er, Eu, S P, Er, Eu, S P, S 4 Materials and Methods Florets were collected in September, 1968 and March, 1 9 & 9 from populations of 0 . hendersoni near Coluckum Pass in NE Kittitas Co., Washington and from transplants of these populations growing in.ithe Botany Garden at the University of British Columbia. They were fixed in a formalin-acetic acid-alcohol solution, dehydrated in a tertiary butyl alcohol series, and embedded in Paraplast, according to the method described by Jensen ( 1 9 6 2 ) . Sections of over 5 5 0 florets were cut at 7-lC>< and stained in safranin, tannic acid, orange G, and iron alum (Sharman 1943)• Drawings were traced off a projection head with the dorsal side to the right except where noted. All sections are radial except where noted. Whole florets were prepared for photography according to the method described by Sattler (1968). •5 Results and Discussion Leaves and Stems--------There are three constant differences between the early development of leaves and that of stems in 0. hendersoni»' Leaves initiateiLby periclinal divisions in the protoderm (Fig. l ) . whereas stems initiate by periclinal divisions in the hypodermis (Fig. 5). Leaf initiation spreads around the axis, giving a crescent-shaped and finally a collar-shaped primordium, whereas the stem primordium is hemispherical. Early growth of the leaf is due to divisions in its protoderm and ground meristem (Figs. 2,3, and 4) , whereas almost a l l the protodermal divisions of the young branch are anti° clinal and growth in bulk is due to divisions in the ground meristem (Figs. 6,7» and 8). ' General Floret Morphology The lemma is the fir s t organ to develop following initiation and early growth of the two glumes. It initiates on the dorsal side (Fig. 9)» Next, the palea initiates on the ventral side (Fig. 10). One stamen initiates on the dorsal side (Fig. 10), and the other two stamens initiate on the lateral sides. A dorsal lodicule initiates on each side of the dorsal stamen. (Fig. 12a). Finally, the ventral lodicule initiates on the ventral side and the carpel initiates on the dorsal side (Fig. 11). There are two vascular bundles entering the floret. The procambium on the dorsal side, which goes only to the lemma, is the fi r s t to develop (Fig. 10). By the time i t has joined with the vascular system of the pedicel, the procambium of the rest of the flower has initiated (Fig. 11). Carpel initiation encircles the floral apex (Fig. 13), the awn differ-entiates (Figs. 12-15e) and the ovule becomes hemianatropous (Figs. 16-18). 6 Lemma The lemma initiates by periclinal divisions in the protoderm (Fig. 19), which spread around the axis to give a collar-shaped primordium (Figs, 79 and 80). Early growth is the result of divisions in the protoderm and ground meristem (Figs. 2 0 - 2 2 ) . Thus, the lemma has the early developmental features of a leaf. Awn The dorsal part of the lemma grows much faster than the lateral or ventral parts (Fig. 7 9 )• After this dorsal extension reaches a length of about 2 0 0 ^ (Fig. 2 7 ) , periclinal divisions in the ground meristem initiate the differentiation of the base of the awn (A in Figs. 28 and 2 9 ) from the apex of the lemma (L in Figs. 28 and 2 9 ) . At a later stage, the apex of the lemma is further differentiated by periclinal divisions in the protoderm (Fig. 3 0 ) . As in 0 . mileacea (Maze et al. in prep.) there is no early differentiation of sclerenchyma mother cells in the awn. However, unlike 0 . mileacea, the lemma does not extend above the rest of the floret until carpel initiation has encircled the apex (Fig. 14)» Callus Divisions in the ground meristem at the dorsal base of the lemma begin about the time of carpel initiation (Fig. 3 1 ) . These are followed by many more divisions and cell enlargement in the ground meristem and by a few divisions and cell enlargement in the protoderm (Fig. 3 2 ) . A definite abscission zone is produced by a series of anticlinal divisions in the ground meristem below the callus. Finally, the cells of the ground meristem 7 enlarge even more and form intercellular spaces, while the protoderm and abscission zone cells enlarge and become sclerified (Fig. 33 )• Palea The palea initiates by periclinal protoderm divisions (Fig. 2 3 ) , which gradually encircle the stem. Its early growth is a result of divisions in the protoderm and ground meristem (Figs. 24, 25 , and 2 6 ) , However, fewer periclinal divisions result in a thinner organ than the lemma and leaf, and slower anticlinal divisions result in slower early elongation. Lodicules The ventral lodicule initiates in the protoderm (Fig, 34)» "but the divisions do not spread more than a tenth of the way around the stem. The resulting primordium is oblong in cross section (Fig, 1 2 a ) . Early growth results from divisions in the protodermal cells and the few cells of the ground meristem (Figs. 35-37)* There are very few periclinal divisions resulting in an even thinner organ than the palea, but its early elongation is at about the same rate as that of the palea. The dorsal lodicule is unique in that i t initiates by divisions in the protoderm and hypodermis (Fig. 38)• The young primordium is hemispherical, and early growth is due to divisions in the protoderm and ground meristem (Fig. 3 9 - 4 2 ) . Thus the ventral lodicule is like a leaf in initiation and early growth but more like a stem primordium in shape. The dorsal lodicule is intermediate in.initiation, like a leaf in early growth, and like a stem primordium in shape. The assertions that the lodicules of 0. hendersoni are modified 8 petals, modified bracts, modified stamens, or the result of fusion of two of these structures are a l l equally probable in light of present evidence. Stamens The stamens initiate by divisions in the hypodermis (Fig. 43)<> The initiations do not spread and the young primordium is hemispherical (Fig. 80). Early growth is due to divisions in the ground meristem (Figs. 44-49). Thus, the stamen is similar to the stem in early development. The anther wall is of the monocotyledonous type (sensu Davis 1966), since the inner layer of cells divides to give the middle layer and the tapetum (Fig. 51 )• Just before these divisions, a few vacuoles appear in the nucleoli of some of the sporogenous cells (Fig. 50)« Just following the divisions, every sporogenous cell has one or a few small vacuoles (Fig. 51)» which eventually grow and/or coalesce to form single, large nucleolar vacuoles- (Fig 52). Gynoecium The carpel initiates by periclinal divisions in the protoderm on the dorsal side of the floral apex (Fig. 53)• The divisions gradually encircle the apex until they are seen on the ventral side (Fig. 55)• Early growth results from divisions in the protoderm and ground meristem (Figs. 54-56). Thus, the carpel is similar to the leaf in early development. The ovule develops directly from the floral apex. Although the i n i t i a l orientation of the ovule is nearly basal (Fig. 56), series of divisions at its base gradually push i t to a lateral position (Fig. 57)• A style develops from each lateral wall of the carpel, and parenchyma, elongated parallel to the carpel edges, fuses the carpel edges together (Fig. 81). After fertilization, 9 the carpel1,, .•« hut not the fusion tissue, becomes f i l l e d with starch (Fig. 82), and the styles drop off. This developmental evidence supports the conclusion of Sharman (i960) that grasses have one carpel. The developmental evidence of 0. hendersoni also supports previous studies in the Gramineae (Barnard 1955, 1956; Mehlenbacher and Maze 1970) which have demonstrated that the grass ovule is stem-borne since i t develops directly from the floral apex and not from the carpel. Integuments The integuments are leaflike since they initiate from divisions in the protoderm which rapidly encircle the floral apex (Fig. 57, 60, and 61). However, unlike successive leaves, which alternate in their position of initiation, both integuments initiate on the dorsal side and spread ventrally. There is one additional series of spreading divisions which do alternate for the two integuments. The outer integument is three cells thick on the ventral side almost from the time of initiation (Fig. 61). These divisions quickly spread dorsally so; that by dyad stage the outer integument on the dorsal side is also three cells thick (Fig. 63). The micropylar end of the inner integument becomes three cells thick on the dorsal side following dyad stage (Fig. 64). These divisions spread ventrally so that by the time of fertilization the inner integument is three cells thick a l l the way around. This thickened rim of the inner integument forms the microphyle. The walls of the cells of the inner integument do not become safraninophilic as they do in 0. miliacea (Maze et al 1970). On the ventral side of the outer integument, a number of divisions in the middle and outer layers form a large bump (Fig. 66), which eventually extends over 50yu . Just before fertilization, the cells of the outer 10 integument become elongated and vacuolated. By the time the endosperm is cellular, the cells of the outer integument are dead (Fig. 82). Nucellus Development of the nucellus passes through four intergrading phases. First, during, early megasporogenesis, the ovule is pushed from a slight uptilt to a slight downtilt by divisions in the ventral part of the chalaza .(Fig. 62). Secondly, during later megasporogenesis, the nucellus elongates by divisions at the base of the embryo sac (Fig. 64). Thirdly, during early megagametogenesis, as divisions at the base of the embryo sac continue, the ovule is tilted further downward by divisions which produce files of cells in the ventral part of the chalaza.,(Fig. 68). Fourthly, as the divisions in the chalaza decrease, additional elongation takes place as a result of divisions alongside the embryo sac (Figs. 69 and 7 5 ) » Also, series of periclinal divisions in the ground meristem add a bulge to the ventral side of the nucellus (Fig. 7 5 ) • Embryo Sac. Megasporogenesis The number ( 3 - 6 ) and arrangement of cells in the nucellus with dense cytoplasm and large nuclei is not constant (Figs. 57-60). Such multicellular archesporia are usually considered excess baggage (Cronquist 1968, p. 108) and, like the massive nucellus, do not correlate with the supposed great reduction of the grass floret. One archesporial cell functions directly as the megaspore mother cell (Fig. 61), while the others resume normal appearance and divisions. The megaspore mother cell divides to give the dyad (Figs 62 ,11 and 6 3 ) . The inner cell of the dyad divides before the outer (Pig. 6 4 ) . Of ten slides showing the tetrad stage, eight showed that the outer cell had divided in a plane perpendicular to the inner, giving a T-shaped tetrad (Fig. 6 7 ) . The other two were linear (Fig. 6 6 ) . Commonly, the basal cell is larger than the other three and may be the one eventually to function as the megaspore. Megagametogenesis The megaspore undergoes three synchronous nuclear divisions to give an eight nucleate embryo sac (Fig. 6 9 ) . Cell walls are formed around three nuclei at each end (Fig. 7 0 ) . The free nucleus at the micropylar end moves to the chalazal end as the antipodals start to proliferate (Fig. 7 1 ) • After further antipodal proliferation, the two free nuclei migrate to the center of the embryo sac (Fig. 7 2 ) . This is not in agreement with the common assumption that the two nuclei drift to the center synchronously in a l l Polygonum types (Gerrassimova 1 9 6 l ) . Although nucleolar vacuoles were seen as early as tetrad stage (Fig. 6 4 ) , i t i s during this stage of polar nuclei migration that they are fairly constant features in the polar nuclei and the egg. They are small at f i r s t , but may be single or multiple (Figs. 7 0 and 7 2 ) . By fertilization, they have expanded and/or coalesced to form a vacuole which is at least half the diameter of the nucleolus (Fig. 7 3 , 7 5 , and 8 3 - 8 5 ) . Rarely (Fig. 7 4 ) » nucleolar vacuoles are absent. According to Brown and Bertke ( 1 9 6 9 , p . 3 2 2 ) , the significance of these vacuoles is s t i l l unknown. Perhaps the fact that they occur only in sporogenous cells of both stajnen and ovule in 0 . hendersoni is significant. The synergids lack vacuoles and a filiform apparatus, and both synergids 12 degenerate well before fertilization ( F i g o 73 )• unlike 0. miliacea, there are no starch grains in the egg. Fertilization The pollen tube enters through the micropy.le, after the polar nuclei have fused, and discharges its contents into the degenerating synergids (Fig. 7 6 ) . The shape of the embryo sac after fertilization is oblong as in Stipa to r t i l i s (Maze ejb al. 1 9 7 0 ) . Th© nucleoli of the endosperm nuclei have many small vacuoles (Figs. 76, 77> 86 ) 9 and the nucleolus of the zygote has a single, small vacuole (Fig. 7 6 ) . The Nuclear endosperm develops faster than the embryo, the nucleolar vacuoles disappear, and the antipodals eventually separate and degenerate (Fig. 78)• The nuclei of the endosperm become separated by cell walls at a later stage© 13 Discussion of Homology If homology is defined as phonetic similarity (Sattler 1966'0. Sokal and Sneath 1963»> p© 69)©we could say that the lemma and palea ar© homologous to the leaf* However,, the word homology usually has evolutionary implica-tions© Simpson (l96lo p<> 78) and Meeuse (19660 p. 23) define homologous structures as those that are similar due to inheritance from a common ances-tor* Inheritance from a common ancestor can only be demonstrated by objec-tive analysis of the fossil evidence* In the ab sence of fossil evidence9 Meeuse (l966 B.p 0 40 ) has proposed that common ancestry be hypothesized, but that the hypothetical nature of the ancestry be freely admitted© Simpson (1961, p<> 92) has proposed that© in the absence of fossil evidence,, homology can be recognized with varying degrees of probability from phenetic similarity© However,, he admits that such speculation can be confirmed only by fossil evidenceo Unfortunately© i f fossil evidence is not immediately forthcoming,, hypothetical phylogenies have a way of becoming generally accepted© A case in point is the Angiosperm gynoecium. Even in light of contrary phenetic evidence (Mehlenbacher and Maze© in review), i t has been assumed that a l l Angiosperm ovules are carpel borne© Moreover, in the absence of fossil evidence© i t has been asserted that these fertile carpels have evolved from infolding fertile leaves. This assertion has been so well accepted that Cronquist (1968© p© 44) has rejected the Bennettitales and Caytoniales as possible Angiosperm ancestors because they did not have leaf-like sporophyllso The interpretations of the grass lodicules and carpel have also been confused by claims of homology based on hypothetical phylogenies. Arber (1934, p© 149) stated that the lodicules could be regarded as reduced perianth structures i f the typical monocotyledonous floral diagram were 1 4 used as a hypothetical framework. However, subsequent authors have silently assumed that the grasses did in fact evolve from a l i l y - l i k e ancestor and have claimed that the lodicules are homologous to reduced perianth structures (A.S. Hitchcock 1 9 5 0 , p . 9 } Lawrence 1 9 5 1 , P« 3 8 9 ; Gould 1 9 6 8 , p. 5 4 ) . However, there is no evidence that the grasses evolved from a l i l y - l i k e ancestor. Moreover, a l l grass lodicules are not phenetically similar to foliar perianth structures. Stamen-like lodicules occur in Cephalostachyum and Schizostaehyum (Arber 1 9 3 4 » P» 3 9 7 ) , and we have observed the presence of partially stem-like lodicules in 0 . hendersoni. Although the carpel develops as one continuous leaf-like structure in 0 . hendersoni and other grasses (Sharman i 9 6 0 , Barnard 1 9 5 5 ' , Maze e_t a l . in prep.), i t has been assumed that the carpel is homologous to three l i l y - l i k e carpels. Therefore, any aspect of the carpel which appeared in threes was readily accepted as valid evidence for this homology. Arber ( 1 9 3 4 , p. 1 5 2 ) and Gould ( 1 9 6 8 , p. 5 6 ) use the presence of three vascular traces as evidence for three carpels. Eames ( 1 9 6 1 , P» 2 2 2 ) has discussed the absurdity of assuming that each vascular trace represents an organ. In addition, other obviously single carpels have three vascular traces (Tucker and Gifford 1 9 6 6 ) . The fact that there are two or three styles and stigmas in grasses is also sometimes used as evidence for more than one carpel (Barnard 1 9 5 7 ) * However, to assume that the number of styles and stigmas must always be equal or less than the number of carpels is inconsistent with data from many families, (Lawrence 1951)• Some families sometimes have more than one style per carpels Crossosomataceae ( l carpel, 2 styles, 2 stigmas), Portulacaceae ( 2 - 3 , 2 - 5 , 2 - 5 ) , Anacardiaceae ( 3 , 1 - 6 , 1 - 6 ) . Other families have more than one stigma per carpels Zosteraceae 15 ( l , 1, 2 ) Najadaceae ( l , 1, 2 - 4 ) » Datiscaceae (3 ' , ; 3» 6 ) , Droseraceae (3 -5» 3-5, 3-10)> Boraginaceae ( 2 , 1, 1 - 4 ) , Goodeniaceae ( 2 , 1, 2 - 3 ) , Asclepiadaceae ( 2 , 2 , 5 lobed), and Lauraceae ( l , 1, 2 - 3 lobed). Therefore, the facts are that there are stem-borne and leaf-borne ovules in the Angiosperms. This is consistent with the theory that the angiosperm gynoecium has evolved in different ways at different times (Mehlenbacher and Maze, in review). The facts are that grass lodicules are variable and sometimes intermediate. This is consistent with the theory that grass lodicules have evolved at different times from stamens, foliar organs, or from fusion of two organs. The facts are that the grass carpel develops as a single, continuous structure and is vascularized like any other single carpel. This is consistent with the theory that the grass carpel has evolved from a single structure (Meeuse I 9 6 6 , p. 181). Misinterpretations of the facts have resulted from unfounded claims of homologies. Therefore, i t seems that the concept of homology is quite muddled. It means completely different things to different people and often gives rise to misleading hypothetical phylogenies. Furthermore, once the. iphenetic or phylogenetic facts are known, the word homology is superfluous. The statements "organ A is similar to organ B" and "organs A and B evolved from organ C1' are simpler, more precise, and convey more information than such statements as w organs A and B are topographically homologous" and organs A and B are phylogenetically homologous . Therefore, since the word homology is not only ambiguous and misleading but also imprecise and uninformative, i t should not be used. 1 6 Taxonomic conclusions A comparision of the results of this study with those reported by Maze, Bohm, and Mehlenbacher ( 1 9 7 0 ) and Maze, Dengler, and Bohm (in prep.) is presented in Tables II and III. When this comparison is combined with that resulting from previous research (Fig. I), twenty-nine distinguishing characters result. Sixty-nine percent of these are characteristic of Stipa, fourteen percent of Oryzopsis. and seventeen percent are unique. Preliminary investigations of Stipa lemmonii indicate that i t is even more like 0. hendersoni than is S. t o r t i l i s . Because of this high degree of developmental and embryological affinity to Stipa and because 0. hendersoni forms viable hybrids with Stipa lemmonii in the field, i t is proposed that 0. hendersoni Vasey be transferred to Stipa. and: be called Stipa  hendersoni (Vasey) Mehleribaeher© Table I I . Summary and comparison of results? Early floret development Affinities of Character 0. miliacea (o) S. tortilis (s) 0. hendersoni 0. hendersoni Ventral floret procambiums initiation time After carpel initiation Before carpel initiation Before carpel initiation Lemmas Position Time lemma extends above floret Lower Before carpel initiation encircles stem Near apex After carpel initiation Lower After carpel initiation encircles stem encircle stem 0 S Protoderm divisions None at apex Awns Number of ground Feif meristem division Sclerenchyma mother Absent cells Many Many Present Many Many Absent S S Callus s Number of ground meristem divisions Taploid cells Dorsal lodicules initiation time Ventral locicule: initiation time Pew Absent At carpel initiation Before carpel initiation Many Present At carpel initiation Before carpel initiation Many Present Before carpel initiation At carpel initiation S Unique Unique Stamens nucleolar vacuoles Absent in sporogenous cells Gynoeciumt Position of initiation Near apex of carpel on ventral side Present Level with carpel on Present Level with carpel on dorsal side, dorsal side. Intercalary growth at base of ovule Absent Present Present 18 Table III. Summary and comparison of results* Embryology Character 0. mileacea (O) S. tor t i l i s ( s ) .  Affinities of 0. hendersoni 0. hendersoni Integuments s Outer s Persistence Number of bumps Height of bump Inner Obliterated Two 5 Safraninophilic Persits One 5 . Not saf. Persists One 50 Not saf. S S Unique S Nucelluss . _ Relative development of multiple epidermis Cytological changes in cells adjacent to embryo sao Present Absent Absent Embryo Sac: Shape after fertilization Obovate Starch in egg Filiform apparatus Synergid vacuoles Number of degenerated synergids Nucleolar vacuoles Endosperm Present Present Absent One Absent Atypical Nuclear Oblong Absent Present Present One Present Typical Nuclear Oblong Absent Absent Absent Two Present Typical Nuclear S S Unique 0 Unique S S 19 Bibliography Arber, A. 1934* The Gramineae. Cambridge at the University Press. Barnard, C. 1955• Histogenesis of the inflorenscence and flower of Triticum aestivum L. Aust. J. Bot. 5 : 1 - 2 0 . , C. 1957* Floral Histogenesis in the Monocotyledons. I. The Gramineae. Aust. J. Bot. 5« 1 - 2 0 . Bigelow, R.S. 1 9 5 8 . Classification and phylogeny. Syst. Zool. 7'49-59. Brown, W.V. and E.M. Bertke. 1969. Textbook of cytology. CV. Mosby Company, Saint Louis. Cronquist, A. 1 9 6 8 . The evolution and classification of flowering plants. Houghton-Mifflin Co., Boston. Davis, G.L. I 9 6 6 . Systemetic embryology of the Angiosperms. John Wiley and Sons, Inc., New York, London, Sydney. Eames, A. I 9 6 I Morphology of Angiosperms. McGraw-Hill Book Company, Inc., New York, Toronto, London. Gerassimova-Navashina, H. I 9 6 I . Fertilization and events leading up to fertilization. Phytomorphology 1 1 » 1 3 9 - 1 4 6 . Gould, F.W. 1 9 6 8 . Grass systematica. McGraw-Hill Book Company, Inc., New York, Toronto, London. Hitchcock, A.S. 1950* Manual of the grasses of the United States (revised by A. Chase). U.S. Dept. Agr. Misc. Publ. 2 0 0 , Washinton, D.C. 2 0 Hitchcock, CL., A. Cronquist, M. Ownbey, and J.W. Thompson. 1969. Vascular plants of the Pacific Northwest. Part One. University of Washinton Press, Seattle and London. Jardine, N. 1 9 6 9 * The observational and theoretical components of homology. Biol. J. Linn. Soc. Is 3 2 7 - 3 6 1 . Jensen, W. 1 9 6 2 . Botanical histochemistry. W.H. Freeman and Company, San Francisco, London. Johnsono B.L. 1 9 4 5 a Cytotaxonomic studies in Oryzopsis. Bot. Gaz. 1 0 7 . 1 9 4 5 & Natural hybrids between Oryzopsis hyroeniodes and several species of Stipa. Amer. J. Bot. 3 2 J 5 9 9 _ 6 0 8 . ' 1 9 6 2 . Natural hybrids between Oryzopsis and Stipa II. Oryzopsis hymeniodes x Stipa nevadensis. Amer. J. Bot. 4 9 * 5 4 0 - 5 4 6 . • I 9 6 3 . Natural hybrids between Oryzopsis and Stipa III. Oryzopsis hymenoides x Stipa pinetorum. Komarow, V.L. (Editor) 1 9 3 4 « Flora of the U.S.S.R. Vol. II. Lawrence, G. 1 9 5 1 * Taxonomy of vascular plants. The Macmillan Company. New York. Linnaeus, C. 1 7 5 3 • Species Plantarum. Vol. I. Stockholm. Maze, J.R., L. Bohm, and L.E. Mehlenbacher. 1 9 7 0 . Embryo sac and early ovule development in Oryzopsis miliacea and Stipa t o r t i l i s . Can. J. Bot. 4 8 : 2 7 - 4 1 . — — — , N.G. Dengler, and L. Bohm. In prep. Floret development in Oryzopsis miliacea and Stipa t o r t i l i s . 2 1 Maze,'J.P.., N.G. Dengler, W.R. Hildreth, and R. Myatt. I966. The reduced awns of some members of the genus Stipa and their possible relationship to dispersal mechanisms. Amer. J. Bot. 5 3 s 6 3 2 . Meeuse, A.D.J. I966. Fundamentals of phytomorphology. The Ronald Press Company. New York. Mehlenbacher, I.E. and J.R. Maze. 1 9 7 0 . A reappraisal of the Angiosperm gynoecium. B i o l . J. Linn. Soc. (In Review) Sattler, R. 1 9 6 6 . ' Towards a more adequate approach to comparative morphology Fhytomorphology 1 6 : 417-429. Sattler, R. 1 9 6 8 . A technique for the study of f l o r a l development. Can. . J. Bot. 46: 720-722. Saunders, E.R. 1 9 2 5 . On carpel polymorphism. I. Ann. Bot. 39s 1 2 3 - 1 6 ? . Sharman, B.C. I960. Developmental anatomy of the stamen and carpel primordia in Anthoxanthum odoratum. Bot. Gaz. 121: 192-198. Simpson, G.G. I 9 6 I . Principles of animal taxonomy. Columbia University Press. New .York and London. Sokal, R. and F. Sneath. I 9 6 3 . Principles of numerical taxonomy. W.H. Freeman and Company. San Francisco, London. Spellenberg, R. 1 9 6 8 . Notes on Oryzopsis hendersoni (Gramineae). Madrono 1 9 : 283-286. Tucker, S.C. and E.M. Gifford, Jr. 1 9 . 6 6 . Carpel development in Drimys lanceolata. Amer. J. Bot. 5 3 : 6 7 I - 6 7 8 . Vasey, G. 1 8 9 3 * Description of new or noteworthy grasses from the United States. Contr. U.S. Nat. Herb. 1: 267-280. 22 F i g s . 1-8o L e a f a n d s t e m i n i t i a t i o n a n d e a r l y d e v e l o p m e n t F i g . 1 , L e a f I n i t i a t i o n . X J O O . 2-4. E a r l y l e a f d e v e l o p m e n t . X300. 5* I n i t i a t i o n o f b r a n c h o f i n f l o r e s c e n c e . X300. 6-8. E a r l y g r o w t h o f b r a n c h o f i n f l o r e s c e n c e . X J O O . 23 Figs. 9-18 General floret morphology Fig. 9« Young floret X40. L, lemma initiation. 1 0 . Young floret. X40. P> palea initiation; S, stamen initiation. 11. Young floret X40. 7, ventral lodicule initiation; C, carpel initiation on dorsal side. 12 Young floret. X40. 1 2 a . Cross section of young floret as shown in Fig. 12. X40. 7, y•=.£•.''. 1 D, dorsal lodicules; V, ventral lodicules. . 13. Young floret. X40. C, carpel initiation on ventral side. 14. Young floret. X40. 15. Mature floret. X40. 15a. Cross section of mature floret as shown in Fig. 15. X40. 15a-d. Cross section of lemma of mature floret as shoan in Figo 15< 16-18. Mature floret. X 4 0 . 2*> Figs. 19-26. Lemma and palea initiation and early development. Pig. 19. Lemma initiation. X4OQ. ' 2 0 - 2 2 . Early lemma development. X400. 23. Palea initiation. Ventral side on right. X400. 24-26. Early palea development. Ventral side on right. X400 r o ro 25 Figs. 27-35» Differentiation of awn base, lemma apex, and calluso Fig. 27. Lemma before differentiation X300. V, vascular tissue. 28. Initiation of differentiation of awn base and lemma apex. X3OO. V, vascular tissue? A, awn; L. lemma. 29. Differentiation of awn base and lemma apex. X300. v:.:;: A, awn; L, lemma$ V, vascular tissue. 30. Further differentiation of lemma apex. X300. V, vascular tissue. 31. Initiation of callus. X3OO 32-33. Callus development. X3OO. 26 Figs. 3 4 - 4 2 . Lodicule initiation and development. Fig. 3 4 . Ventral lodicule initiation. Ventral side on right X3OO. 35-37• Early ventral lodicule development. Ventral side on rigfefc~ X300 38. Dorsal lodicule initiation. X300. 3 9 - 4 2 . Early dorsal lodicule development. X300. \ 39 2 7 Pigs. 43-52. Stamen initiation and development. Fig, 4 3 . Stamen initiation, X 4 0 0 . 44-46. Early stamen development. X400. 47-49. Early stamen development. Tangential section. X400. 50-52. Anther wall formation and development of nucleolar vacuoles. X400. 45 28 Pigs. 53-59. Carpel initiation and early development. Integument and archesporia initiation. Fig* 53 Carpel initiation on dorsal side. X400. C. carpel; A. floral spex; V, ventral lodicule initiation; P, palea 0 5 4 « Early carpel development on dorsal side. X400. C, carpel; A, floral apex8 V, ventral lodicule. 55» Carpel initiation on ventral side. Early carpel development on dorsal side. X400. C, carpel; A, floral apex. 5 6 . Early carpel development on dorsal and ventral sides. X400. 5 7 . Series of divisions pushing ovule into lateral position.' Integument initiation. Archesporial cells. X 4 0 0 . 5 8 - 5 9 . Archesporial cells. X 4 0 0 . 2 9 P i g S o 60-67* Megasporogenesis. Pig. 60-63. Early megasporogenesis. X400. 64-67. Late megasporogenesis. X400. 30 Figs. 68-74» Megagametogenesis. Fig. 68. Early megagametogenesis. X400. 69-74. Late megagametogenesis. X400, 31 Figs. 75-78. Late Megagametogenesis and Fertilization-Fig. 75<> Late megagametogenesis. X400. 76. Immediate post-fertilization. X40Q. 77-78. Late post-fertilization. X400. 32 79» Young florets. Ventral side on right. X175* Gi, fi r s t glume; G2, second glume; L, lemma . 80. Young florets. Lefts Ventral side facing camera Rights Dorsal side on right. ' A, awn; L, lemma; S, stamen; P, palea X175. 81 Carpel fusion tissue. X200. 82. Starch-filled carpel and dead, pointed outer integument. X125» 83-84* Vacuolated nucleoluc of polar nucleus before fusion. X2000. 85. Vacuolated nucleolus of polar fusion nucleus. X2000. 86. Vacuolated nucleolus of dividing early endosperm. X2000. 

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