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Cyto-morphological study of Prasiola meridionalis Akintobi, Samuel Oyewole 1961

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CYTO-MORPHOLOGICAL STUDY OF PRASIOLA MERIDIONALIS by SAMUEL OYEWOLE AKENTOBI, B.A.(Hons.) A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of BIOLOGY AND BOTANY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November, 1961 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 i t freely available for reference and study. I further agree that 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 allo\^ed without my written permission. Department of BIOLOGY AND BOTANY The University of British Columbia, Vancouver 8 , Canada. Date ^ December 1961 i i ABSTRACT A cu l tu re study o f the morphology, cyto logy and l i f e cyc le of P r a s i o l a mer id iona l i s was conducted. The a lga was grown suc ce s s fu l l y i n P rovaso l i ' s cu l ture medium (1958) a t a temperature of 5 ° C t and alternate periods of eight hours o f l i g h t and s ix teen hours o f darkness. In cu l ture , .gametes are l i b e r a t e d only when mature reproduct ive or f r u i t i n g t h a l l i are f i r s t i l l um ina ted f o r two hours with f luorescen t l i g h t and then kept i n the dark f o r seve ra l hours a t temperatures o f 3°- 5 °C. The r e s u l t s o f the study have i nd i c a t ed that the l i f e cyc le presents a dimorphic a l t e r n a t i o n of generat ions . The gametophytic t i s sue and gametes represent the hap lo id generat ion , and the sporophyt ic t i s sue and zygote the d i p l o i d genera t ion . Meios is i s intermediate i n the l i f e c y c l e , occurr ing i n the adu l t sporophyt ic c e l l s . S ixteen chromosomes were observed i n the d i p l o i d c e l l s , zygote, aplanospores and somatic c e l l s . Sexual reproduct ion i s oogamous. The b i - f l a g e l l a t e micro-gamete i s smal ler than the macro-gamete which has no f l a g e l l a . Asexual reproduct ion i s accomplished by germination o f aplanospores. T h a l l i which develop from germination of aplanospores and from zygotes appear the same morpho log ica l l y . i i i TABLE OF CONTENTS 1 • Abstract i i 2 . Table of Contents i i i 3. Acknowledgment iv !+» Introduction 1 5 . Materials and Methods 4 6 . Observations 8 7. Discussion 8 . Summary 2 0 9. Bibliography 21 10. Table I 24 1 1 . Explanation of Abbreviations 2 5 1 2 . Figures 2 6 i v ACKHOWLEDGMEMT The writer wishes to express his sincere thanks to Dr. Kathleen Cole for the unrestricted assistance given, without which the following experimental study would have suffered greatly. Her kindness, i n t e r e s t and constant willingness to help, discuss and suggest made t h i s study possible. Many thanks are due to Dr. R.F. Scagel for (1) making available to the writer a c o l l e c t i o n of Prasiola meridionalis (the f i r s t material of Prasiola meridionalis with which the writer was acquainted) f o r t h i s study, (2) i d e n t i f y i n g further collections made by the wr i t e r , and f o r (3) h i s suggestions and c r i t i c i s m of t h i s work. The writer acknowledges wth gratitude the help, d i r e c t and in d i r e c t , given by Dr. T.M.C. Taylor, Professor and Head of Department, and other Faculty members of the Department of Biology and Botany. 1 INTRODUCTION. Although the genus Prasiola has been known since early i n the 19th century, Prasiola meridionalis Setchell and Gardner was unknown u n t i l a century l a t e r . In 1920, Gardner (No. 3824).collected and Setchell and Gardner (1920) described the species from Neah Bay, Washington. They reported the presence of aplanospores i n the t h a l l u s . U n t i l the present investigation, no report has been made of number of chromosomes of t h i s species, or i t s l i f e cycle including i t s methods of reproduction. The present study was undertaken to report on i t s morphology, cytology, and l i f e cycle i n culture. Agardh was the f i r s t to describe the genus Prasiola i n 1822, but he was uncertain whether to c a l l i t a t r i b e or sub-tribe of Ulva. In 1838, Meneghini considered i t as an independent genus, Pr a s i o l a . Several species of Prasiola have been described since then. In 1889 De Toni l i s t e d twelve species. Smith (1955) reported twenty species, indicating also that Prasiola i s widely dis t r i b u t e d , some species being marine ad others freshwater. Tatabe (1891) was the f i r s t to describe P. .japonica Yatabe. Yabe's manuscript on the species was published posthumously by I s h i i i n 1932. P. .japonica i s the only species found i n Japan. Eight species have been reported on the P a c i f i c coast of North America. Four of these species, P. crispa (Lightfoot) Agardh, P. borealis Reed, P. delicata Setchell and Gardner, and P. meridionalis Setchell and Gardner are s t r i c t l y marine; P . f l u v i a t i l i s (Sommerfelt) Areschoug, P # mexicana Agardh, P, nevadensis Setchell and Gardner, are / 2 found e n t i r e l y i n co ld freshwater streams; and P. ca lophy l l a Meneghini , a l though t e r r e s t r i a l , i s found i n a marine l o c a l i t y . P. s t i p i t a t a Suhr was f i r s t descr ibed by Suhr i n 1831, but i t was not s tud ied i n d e t a i l . Drew d i s t i ngu i shed the gametophytes among mate r i a l c o l l e c t e d i n Bangor, North Wales i n 1955* She v e r i f i e d the m o t i l i t y and f u s i o n o f the gametes i n February, 1956, and i n the fo l lowing year a l l her observat ions and those o f her co-worker Friedmann were j o i n t l y pub l i shed under the t i t l e "Occurrence o f Gametes i n P. s t i p i t a t a Suhr" (Drew and Friedmann, 1957). Friedmann (1959) undertook a more d e t a i l e d i n v e s t i g a t i o n o f the development and l i f e h i s t o r y o f the spec i e s . In i960, Friedmann and Manton, with the a i d of an e l e c t ron microscope, s tud ied ex tens i ve l y the gametes, f e r t i l i z a t i o n and zygote development of the spec i e s . E a r l y workers s tud ied the morphology and asexual reproduct ion o f soffie species o f P r a s i o l a . Knebel (1936) s tud ied the morphology of P. c r i s p a . He a l s o repor ted that Jessen, i n h i s monograph o f 1&+8, descr ibed the morphology o f seve ra l spec ies i nc lud ing P. s t i p i t a t a . Gay (1888), Lagerheiro (1892) and W i l l e (1901, 1906) d iscussed the vegetat ive reproduct ion o f P r as io l a by what they considered "gemmation of fronds and ak i ne t e s " ; In 1895 Bo rz i reported b i - f l a g e l l a t e zoospores i n the l i f e cyc le of P r a s i o l a . A l l the workers before 1931 agreed that P r a s i o l a could propagate i t s e l f a sexua l l y . Unl ike the repor t of asexual reproduct ion , the one r e l a t e d to sexual reproduct ion was most con t ro ve r s i a l , be ing v i o l e n t l y denied 3 and rejected by some investigators. Newton (1931) described the thallus and concluded that "sexual reproduction i s unknown i n Pr a s i o l a " . Yabe (1932) remarked that both micro- and macro-gametangia are formed on the same frond. He reported the fusion of b i - f l a g e l l a t e micro- and macro-gametes. Several workers including F r i t s c h (195*0 and Smith (1955) rejected the work of Tabe and a l l the previous reports. Uda's report of sexual reproduction i n P. japonica i n 194-8 was confirmed and substantiated with photographs by Fujiyama i n 1955. MATERIALS AND METHODS. P r a s i o l a mer id iona l i s used i n th i s study was c o l l e c t e d between the t i des on rocks and boulders on the P a c i f i c Coast a t F r iday Harbor, Washington on 2 6 Ju ly 1 9 6 0 ; a t Wh i f f in S p i t , Vancouver I s land , B.C. dur ing the months of November and December, 1 9 6 0 ; and a t three l o c a l i t i e s in-Stanley Park, Vancouver, from January through May, 1 9 6 1 . P. mer id iona l i s i s s t r i c t l y marine, and dur ing t h i s study i t has been found growing above sea water on the boulders encrusted by b i r d s 1 f e c e s . P r a s i o l a t h a l l i , found a t low t i de or above water,ars-BPtted together , ho ld ing moisture f o r sometime u n t i l the t i de r i s e s aga in . The t h a l l i are d i r t y green ( f i g s . 1 , 2 ) and a t the f r u i t i n g stage show a l t e rna te dark and l i g h t green patches a t t he i r a p i c e s . The c o l l e c t e d t h a l l i were t r ans fe r r ed to an i ce-coo led conta iner f i l l e d with sea water. In the laboratory they were cleaned c a r e f u l l y with a brush and t r ans fe r r ed to dishes conta in ing cu l tu re medium. They were kept a t temperatures of 5 ° "to 8^0. The cu l tu re media used i n t h i s study were Lewin's a r t i f i c i a l sea water (1955)» s t e r i l i s e d sea water enr iched with phosphates and n i t r a t e s , and P r o v a s o l i ' s medium (1958) modif ied by inc reas ing the amounts o f hormones so that the quan t i t i e s are as fo l lows f o r each 100 m l . o f cu l ture medium: Adenine 3 mi l l ig rams G ibbe re l i n 10 micro-grams K i n e t i n 1 0 micro-grams Indole a c e t i c a c i d 5 micro-grams 5 P r o v a s o l i ' s cu l tu re medium was brought to pH 8.0 or 8.2 . I t gave the best r e s u l t s s ince the t h a l l i cu l tu red i n the medium grew normal ly . Lewin's medium supported the growth o f b a c t e r i a , and was not p a r t i c u l a r l y conducive to the growth of P. m e r i d i o n a l i s . S t e r i l i s e d sea water enr iched with n i t r a t e s and;phosphates supported growth but the t h a l l i became pale and unhealthy. A p e t r i -d i sh was layered with f i l t e r paper soaked with the cu l tu re medium to keep the container mo is t . S l i des were l a i d on the moist paper. The t h a l l i of P r a s i o l a mer id iona l i s were l a i d separate ly and i n d i v i d u a l l y on the s l i d e s ( f i g . 1 ) . Three times each day, drops of the cu l tu re medium were added to the t h a l l i , the moist paper being changed twice a week. The pe t r i -d i sh was covered and p laced i n a r e f r i g e r a t o r a t 5° - 8 ° C . I l l umina t ion was provided by a f l uo rescen t tube suspended over the cu l tu re p l a te i n the r e f r i g e r a t o r g i v ing an i l l u m i n a t i o n o f e ighty foo t candles i n a l t e rna te l i g h t (16 hours) and dark (8 hours) pe r iods . The method employed to a i d the re lease of gametes i s o f p a r t i c u l a r i n t e r e s t . Friedmann (i960) noted that the gametes of P r as io l a  s t i p i t a t a were re leased from the t ha l l u s i f the f r u i t i n g tha l l u s had been kept i n the dark f o r a t l e a s t s ix teen hours . During th i s study, the f r u i t i n g tha l l u s of P. mer id iona l i s was l a i d Oils.a s l i d e and kept i n the dark f o r 16 - 18 hours . A few drops o f the cu l tu re medium were added twice a day. The gametes were re leased a t temperatures vary ing from 4° to 5 °C . Thereaf te r , the s l i d e was rep laced by a new one t h r i c e d a i l y . Once the l i b e r a t i o n of the gametes s t a r t ed i n the dark, the presence or absence of l i g h t had no in f luence on re lease of gametes. 6 Some mate r i a l was f i x e d i n the f i e l d , and some a t i n t e r v a l s a f t e r being cu l tu red i n the l abo ra to r y . Severa l f i x a t i v e s were s a t i s f a c t o r y i f the mate r i a l was thoroughly washed a f t e r f i x i n g . During th i s study, fo rma l in-ace t i c-a l coho l (100 c . c . e thano l , 7 c . c . g l a c i a l a c e t i c , and kO c . c . kofi formaldehyde) gave the best r e s u l t s . Ace t i c-a l coho l ( 1 O ) was s u c c e s s f u l , p a r t i c u l a r l y with the Feulgen s t a i n i ng technique. The f i x e d t h a l l i were kept i n t i g h t l y c losed b o t t l e s i n an oven a t a temperature o f 75^C» f o r about twelve days; the f i x a t i v e was changed every four hours u n t i l the t h a l l i were thoroughly b leached. The t h a l l i were passed through 70$ - 50$ - 30$ a l c o h o l and washed thoroughly i n d i s t i l l e d water. They were sometimes s tored i n 70$ a l c o h o l . Although Karpechenko 1s f i x a t i v e (Dar l ington and La Cour ,196o) bleached the t h a l l i as w e l l , i t requ i red much longer washing, and the r e s u l t obtained d i d not j u s t i f y the time expended. Moreover, t h i s f i x a t i v e i s chemica l ly unstable a f t e r a shor t time even when s tored i n the dark . Therefore , i t i s prepared i n two pa r t s , and mixed jus t before i t i s used . S ta in ing was ca r r i ed out on the whole p ieces of t h a l l u s , gametophytic t i s sue and the zygote . The best r e s u l t s were obtained with propiono-carmine (Dar l ington and La Cour, i 9 6 0 ) which s ta ined the chromosomes more conspicuously than the pyrenoids . One or two drops o f propiono-carmine were added to the t h a l l u s on a c lean s l i d e , and a f t e r f o r t y seconds, a cover s l i p was a p p l i e d . The s l i d e was warmed gent l y over a s p i r i t f lame. Pressure was app l i ed to spread the c e l l s before the cover 7 s l i p was sealed with a paraff in-gum mastic compound. The s t a i n i ng o f the t ha l l u s with modi f ied aceto-carmine (Friedmann 1959» 1960) r equ i red a much longer time but y i e l d e d good r e s u l t s , p a r t i c u l a r l y a f t e r the s t a ined tha l l u s had been c leared i n k$$> a c e t i c a c i d . Feulgen s t a i n ( S to rve l , 195^ $' La Cour, i960) was found appropr ia te only to v e r i f y the presence of nuclear ma te r i a l , s ince the chromosomes were not c l e a r l y de f i ned . During t h i s s tudy, motion p i c tu r e of the gametes, syngamy and the zygote were taken. Photomicrographs were a l so taken us ing 35 rom» Kodak h igh contrast copy and Kodak D-11 developer f o r maxmum con t ras t . P r in t s were made on Kodak bromide F3t s i ng l e weight paper and developed i n c o b r o l . Camera l u c i da drawings were made d i r e c t l y from microscope. 8 OBSERVATIONS. Stages of the l i f e cyc le of P ras io l a mer id iona l i s observed i n cu l tu re dur ing t h i s study inc lude the adu l t t h a l l u s , gametes, syngamy, zygote, the developing stages of the zygote and aplanospores. The genera l type o f l i f e cyc le ( f i g . 3) observed i n _P , mer id iona l i s i s d i p l o-hap lo i d i c s ince a macroscopic d i p l o i d sporophyte a l te rna tes w i th a microscopic hap lo id gametophyte, the two generat ions being morpholog ica l l y d i s s i m i l a r . A more d e t a i l e d l i f e cyc le of P. mer id iona l i s i s presented i n F i g . 4. The micro- and macro-gametes are re leased from the apex o f the t h a l l u s . While the e l l i p s o i d a l micro-gamete i s b i - f l a g e l l a t e the l a r g e , sphe r i c a l macro-gamete has no f l a g e l l a . Syngamy occurs s h o r t l y a f t e r the gametes are r e l e a sed . The zygote undergoes mi tos i s and an obovate t ha l l u s forms fo l low ing fu r the r c e l l d i v i s i o n . The c e l l s a t the apex of the t ha l l u s undergo meiosis to produce hap lo id c e l l s . These c e l l s then d i v i de m i t o t i c a l l y and produce c e l l s which the ra f t e r cons t i tu te the gametophytie t i s s u e . The female and male gametes are produced by c e l l s , i n patches of the gametophytie t i s s u e . The union o f the male and female gametes s t a r t s the l i f e cyc le over aga in . An asexual par t of the l i f e cyc le i s observed s imultaneously as an accessory method of reproduc t ion . The mature c e l l s from the s ide and center o f the t h a l l u s enlarge and d i f f e r e n t i a t e . Each one d iv ides m i t o t i c a l l y to form four or s i x daughter c e l l s , c a l l e d aplanospores, ' a l l contained w i th in the mother c e l l wa l l or a common coat ( f i g . 28 ) . On r e l ease , each aplanospore d i v ides m i t o t i c a l l y i n a manner s i m i l a r to that o f the zygote to form an adu l t t h a l l u s . 9 The adu l t t ha l l u s of P. mer id iona l i s cons i s t ing o f both sporophyte and gametophyte i s obovate i n shape and d i r t y green i n colour ( f i g s . 1,2). I t i s 7 - 17 mm. i n length ( f i g s . 2,5) and i t s width va r i e s from the r h i z o i d to the apex, being about 2 mm. near the base, 8 mm. a t the middle o f the t h a l l u s , and 12 mm. or more a t the apex. The r h i z o i d , the somatic t i s sue and the gametophytic t i s sue are e a s i l y d i s t i n g u i s h a b l e . The shor t co lour less r h i z o i d i s he ld f a s t to the substratum by a mucilaginous substance secreted by the basa l c e l l s { ( f i g s . 6, 7 ) . The somatic t i s sue ( f i g s . 8, 9) i s un i formly dark green i n co lour . I t s c e l l s are of uniform s i z e and are arranged i n an i r r e g u l a r f ash ion ( f i g s . 7, 9 ) . The gametophytic t i s sue a t the apex, or top t h i r d of the t h a l l u s , can be i d e n t i f i e d macroscop ica l l y . I t contains i r r e g u l a r l y shaped patches o f dark green c e l l s a l t e rna t i ng with the groups o f very l i g h t green c e l l s , present ing a mosaic pa t te rn ( f i g s . 8 , 1 0 ) . The dark green c e l l s produce female gametes, and the l i g h t green c e l l s , the male gametes. Unl ike the r h i z o i d a l and somatic t i s s u e s , t h i s t i s sue i s poly-stromat ic being four or s i x c e l l s deep. The patches of the dark green c e l l s are u sua l l y two to four c e l l s deep, and those o f l i g h t green c e l l s are u s u a l l y four to s i x c e l l s deep. The c e l l s of the d i p l o i d part of the tha l l u s are morpholog ica l l y a l i k e but d i f f e r i n s i z e . Each c e l l i s un inuc lea te . The nucleus i s l oca ted near the edge o f the cytoplasmic membrane, next to the green chromatophore and on the same plane wi th i t , but not so e a s i l y seen ( f i g . 1 1 ) . The conspicuous chromatophore i s a x i l e i n p o s i t i o n with f inger-HLike 10 projections radiating towards the periphery of the c e l l . Within the center of the green chromatophore i s a single pyrenoid (figs. 11, 13). The chromatophore i n the basal c e l l i s inconspicuous and the.cells are light green or colourless. The basal cells are the largest i n the thallus, each being 6 - 8 microns long. This variation i n the size of the cells is more conspicuous i n the growing thallus. The diploid somatic cells of the mature thallus average 8.3 microns i n diameter. Two types of c e l l division, mitosis and meiosis, were observed among the cells of the thallus. Mitosis occurs i n the rhizoidal and somatic tissue of the thallus. Meiosis, however, i s restricted to the top or uppermost cells of the sporophytic tissue at the apex of the thallus. At the beginning of mitotic division, the somatic cells enlarge considerably from 8.3 microns i n diameter to 22 microns i n length and 7.3 microns i n width. The nucleus becomes granular with a single nucleolus i n .the center. The chromosomes are seen clearly at the early mitotic prophase but they are not individually distinguishable at late prophase or metaphase. Sixteen chromosomes were counted at early prophase and at metaphase ( f i g . 12). Generally only eight or nine chromosomes were seen in one focal plane. The chromosomes are quite small. The spindle apparatus i s not very distinct at metaphase. At telophase, the chromosomes clump together at the poles of the c e l l . Simultaneously with nuclear division, the pyrenoid divides into two daughter pyrenoids, and the daughter pyrenoids migrate towards opposite poles of the c e l l (figs.13» 1^ ). 11 f The second type of c e l l d i v i s i o n , me ios is , fo l lows the usua l sequence assoc ia ted with reduc t ion d i v i s i o n . During the ea r l y me io t i c prophase, the d i p l o i d c e l l becomes l a r g e r , inc reas ing i n s i z e from 5.6 microns to 7.3 microns i n diameter. The chromatic mate r i a l i s concentrated a t one s ide o f the nuc leus, and the nuc leo lus i s l o ca t ed i n the center o f the nuc leus . A d e f i n i t e nuclear membrane pe r s i s t s throughout the meiot i c prophase s tage. There are many granules i n the c e l l a t ea r l y prophase of f i r s t d i v i s i o n which makes the counting o f the chromosomes qu i te d i f f i c u l t . At the l a t e me iot i c prophase, the chromosomes become v i s i b l e . E ight pa i r s o f chromosomes were counted surrounding the nucleolus ( f i g . 15). The chromosomes clump together a t metaphase so that i n d i v i d u a l chromosomes are i n d i s t i n g u i s h a b l e . The c e l l appears elongated i n anaphase I ( f i g . 16). E ight chromosomes were counted migrat ing towards each pole of a c e l l . At telophase of f i r s t d i v i s i o n the daughter chromosomes are found grouped together a t the opposi te po l e s . Second d i v i s i o n of meiosis fo l lows i n a regu la r manner, so that four hap lo id c e l l s are produced from one d i p l o i d c e l l . The d i v i s i o n of the pyrenoid i n t o two daughter pyrenoids occurs s imultaneously wi th nuclear d i v i s i o n . The gametophytic t i s sue i s formed as the r e s u l t of m i t o t i c d i v i s i o n s of the new hap lo id c e l l s . Th is gametophytic t i s sue i s attached t o , and becomes a part ' o f the t h a l l u s . The t ha l l u s now assumes a d i f f e r e n t morphology. The th ickness o f the gametophytic t i s s u e increases from one to four or s i x c e l l s . The c e l l s form two d i s t i n c t groups, l a rge r dark green c e l l s , and smal ler pa le green 12 ones, present ing patches o f i r r e g u l a r shapes, a l l set i n mosaic pa t t e rn . An outer coat covers the t h a l l u s ( f i g s . 7, 10), and a l s o forms septa among the groups of c e l l s i n the gametophytie r e g i o n . The hap lo id c e l l s o f the gametophytie t i s sue are smal ler than the d i p l o i d somatic c e l l s . They measure, on the average, 6 - 7 microns i n diameter. Hap lo id c e l l s are e a s i l y recognised by the comparatively smal l quant i t y of chromatin they conta in . The smal ler hap lo id c e l l s conta in a smal l chromatophore and appear l i g h t green. The l a r g e r ones conta in a l a r g e r chromatophore, and are dark green i n co lour . Each contains a nuc leus , chromatophore and pyrenoid , occupying the same r e l a t i v e pos i t i ons as i n the d i p l o i d c e l l s . The shape of the chromatophore i s a x i l e , as i n the somatic c e l l s . The dark green hap lo id c e l l s d i f f e r e n t i a t e i n to the macro- or female gametes, and the l i g h t green ones, i n t o the micro or male gametes. When the septa which separate groups o f c e l l s d i s s o l v e , b l adder- l i ke gametangia are formed from the outer coat o f the t h a l l u s . The gametangium i s ruptured, due perhaps to the mechanical pressure exerted on i t by the gametes, and the gametes are re l eased i n hundreds. The macro-gamete i s sphe r i c a l i n shape, and has no f l a g e l l a . I t v a r i e s i n diameter from 2.4 - 4.0 microns . The micro-gamete wi th two f l a g e l l a a t i t s an t e r i o r end i s 1.5 - 2.0 microns i n diameter ( f i g s . 1 7 , 1 8 ) . Each female or male gamete possesses one inconspicuous chromatophore. Two or more micro-gametesmay approach one macro-gamete; but i n t h i s study, only one micro-gamete was observed un i t i ng with the macro-gamete 13 to form a zygote ( f i g . 20 ) . M o t i l i t y o f the zygote was observed u n t i l the gametic union was completed. Syngamy was best demonstrated i n the motion p i c tu re taken dur ing t h i s study. The immobile zygote becomes round and enlarges to 14 or 16 microns i n diameter ( f i g . 20 ) . I t d i v ides m i t o t i c a l l y i n to two, and then four or more c e l l s forming a f i l ament ( f i g s . 20, 21) , the basa l c e l l s developing i n t o the r h i z o i d ( f i g s . 22, 23) . Further d i v i s i o n of the c e l l s i n two planes r e s u l t s f i r s t i n the format ion of the young obovate tha l l us ( f i g s . 22 - 25) , and then o f the adu l t t h a l l u s . Occas iona l l y , groups o f aplanospores are found i n the center and a t the edge ( f i g . 28) of the somatic t i s s u e . Tbose i n t h i s study were found i n o l d t h a l l i f r e s h l y c o l l e c t e d from the sea , or growing i n the cu l tu re medium l e f t unchanged f o r over a month i n a f r eez ing compartment (O^C). Groups of aplanospores were found a l so i n t h a l l i cu l tured i n Lewin's medium brought to the pH of 8.8 - 9.0 ( f i g s . 26 «• 28 ) . An aplanospore re leased i n P r o v a s o l i ' s medium grew and d i v i ded i n a manner smi la r to that of a zygote, forming f i r s t a f i l ament and l a t e r an obovate t h a l l u s . 14 DISCUSSION. L i f e Cycle The l i f e cyc le observed i n P ras io l a mer id iona l i s i s unique i n the p lant kingdom. Although the a l t e r n a t i o n o f generat ions i n t h i s species i s d imorphic , the sporophyt ic t i s sue i s a t tached to and s i m i l a r to the gametophytie t i s sue except i n two f ea tu res . The gametophytie t i s s u e i s poly-stromat ic whereas the sporophyt ic t i s s u e i s mono-stromatic. The gametophytie t i s sue contains green and l i g h t green reproduct ive patches which are not present i n the sporophyt ic t i s s u e . The format ion o f patches conta in ing sex c e l l s i n P. mer id iona l i s has been repor ted f o r the f i r s t time i n the present i n v e s t i g a t i o n . Each o f the patches can be considered a gametangium. The reason f o r assuming so i s that the outer coat which covers the whole t ha l l u s forms septa among the groups of c e l l s . When the septa d i s s o l v e , the po r t i on of the outer coat cover ing the patches becomes a b ladder- l i ke s t ruc tu re or a receptac le conta in ing gametes. According to Clapper (i960) a gametangium i s an enclosed compartment i n which gametes are formed. O r d i n a r i l y , the term i s used only when c e l l s producing gametes are morpholog ica l l y d i f f e r e n t from vegetat ive c e l l s . The c e l l s which produce gametes o f P. mer id iona l i s are hap lo id and they are smal ler than the d i p l o i d vegetat ive c e l l s . Hence the term "gametangia" may be c o r r e c t l y app l i ed to the patches contained i n the gametophytie t i s sue o f P. m e r i d i o n a l i s . 15 The occurrence o f such patches i s not l i m i t e d to P. m e r i d i o n a l i s . The presence of dark and l i g h t reproduct ive areas i n P. .japonica was repor ted by Yabe (1932) and Fujiyama (1955). and i n P. s t i p i t a t a by Drew (195?) and Friedmann (1957, 1959) . Yabe s ta ted that the male or micro-gametangium i n P. japonica produces 64 gametes, and the female or macro-gametangium, 16 gametes. The patches assume var ious shapes i n the three spec i es , but i n each case present a mosaic pa t t e rn . In P. .japonica. the patches form i r r e g u l a r r e c t ang l e s . In P. s t i p i t a t a , they form smal ler r ec tang les , and Friedmann considers them an i r r e g u l a r system of pa i red male and female a reas . In P. me r i d i ona l i s , the patches are irregular i n shape. There are some remarkable d i f f e rences i n the l i f e cyc les o f the freshwater species P. .japonica, and o f the marine species P. mer id iona l i s and P. s t i p i t a t a . Fo l lowing a d e t a i l e d c y t o l o g i c a l i n v e s t i g a t i o n , Fujiyama (1955) concluded that P. japonica i s a hap lont . The term •haplont' expresses the r e l a t i v e length of the hap lo id and d i p l o i d s tages . According to Fujiyama, meiosis takes p lace immediately a f t e r the zygote i s formed, and the p lant a r i s i n g from the reduc t ion d i v i s i o n o f the zygote has the hap lo id number of chromosomes. The zygote, t h e r e f o r e , i s the only d i p l o i d c e l l i n the l i f e cyc le of the spec i es . The formation o f gametophytic or reproduct ive t i s sue i n t h i s haplont i s not explained^ by e i the r Yabe or Fuj iyama. The l i f e cyc les of the two marine spec ies , P. mer id iona l i s and P. s t i p i t a t a are s i m i l a r to each other . 16 Friedmann (1959) descr ibed the l i f e cyc le o f P. s t i p i t a t a as being dimorphic d i p l o - h a p l o i d i c , s i m i l a r to that repor ted i n t h i s study f o r P. m e r i d i o n a l i s . The sporophyt ic generat ion of _P_. mer id iona l i s serves two f u n c t i o n a l purposes. I t provides means f o r both asexual and sexual reproduct ion by producing aplanospores and hap lo id c e l l s which produce gametes a f t e r fu r the r d i v i s i o n . I t i s i n t e r e s t i n g to note that i n t h i s study the t h a l l u s produced by the germinat ion of the d i p l o i d aplanospore, and that produced by the germinat ion of the d i p l o i d zygote appear morpho log ica l l y i d e n t i c a l . One might expect some d i f f e rences i n the t h a l l i produced from the zygote s ince segregat ion and recombination of chromosomes are assoc ia ted wi th gamete format ion and syngamy. The f a c t that no v a r i a t i ons occur i n the t h a l l i may be due to homozygosity o f genes respons ib le f o r these s p e c i f i c characters or due to ra ther i n f l u e n t i a l environmental cond i t i ons . There i s one important c h a r a c t e r i s t i c common to the l i f e cyc le o f the three P ras io l a species : t h e i r oogamous method of sexua l r eproduc t ion . A controversy ex i s ted f o r a long time concerning the existence o f sexual reproduct ion i n P r a s i o l a , and var ious disagreements among the ea r l y wukers about i t s method of sexual r eproduc t ion . Both Uda (1948) and Fujiyama (1955) concluded that oogamy i s the method of sexual reproduct ion i n P. j apon ica . In 1957. Drew and Friedmann publ ished a d e t a i l e d account of sexual reproduct ion i n P. s t i p i t a t a . 17 They reported then that both male and female gametes of P. stipitata are bi-flagellate, and that the type of sexual reproduction i s anisogamous. This account was followed by the conclusion of Friedmann i n 1959 that both gametes are bi-flagellate. However, i n 1960, Friedmann corrected the former statement when Manton, with the use, of electron microscope, noted that only the male gametes possess two f l a g e l l a . In a l l three Prasiola species only the micro-gametes are bi-flagellate. Cytology In the three Prasiola species studied, the diploid cells are larger than the haploid. Both haploid and diploid cells i n P. stipitata are smaller than their counterparts i n P. meridionalis. In, P. .japonica. the zygote, which i s the only diploid c e l l , varies in size from 6 microns i n diameter to 12.4 microns x 19.6 microns. The haploid cells of this species average 7 microns in diameter. The diploid c e l l of P. meridionalis measures 8.3 microns in diameter and the haploid, 6.7 microns. The mitotic and meiotic c e l l division processes observed in Prasiola meridionalis are quite regular and similar to those reported by Friedmann (1959) in £• stipitata. The chromosome number of the three Prasiola species which have been studied cytologically are presented in Table I. I t is interesting to note that the chromosome numbers diff e r and that P. meridionalis ,has the highest number of the three. Factors Affecting?: Gamete Production. Temperature, light, nutritive and climatic conditions appear to be important factors involved in the production of gametes in Prasiola. 18 Yabe (1932) found that sexua l reproduct ion i n P. .japonica occurs gene ra l l y i n the months o f November through A p r i l when cooler water temperature i s conducive to gamete format ion . Uda (1948) a l so found that gametes of P. .japonica are re leased dur ing February when the water temperature i s coo ler (10°- 1 2 °C ) . Smith i nd i ca t ed , the re fo re , tha t there seems to be a c o r r e l a t i o n between temperature and per iods i n which the gametes are formed, not ing that when the temperature i s constant ly the same throughout the year , gamete format ion can take place any t ime. F r i t s c h (1955) surmised that the product ion of sexual c e l l s ensues fo l l ow ing the accumulation of n u t r i t i v e mater ia l and when the cl imax of vegetat ive a c t i v i t y i s passed. I t was es tab l i shed i n the present study that a l t e rna te per iods o f l i g h t and darkness induce the l i b e r a t i o n o f the gametes of P. m e r i d i o n a l i s . Friedmann (i960) repor ted that mature sexual t h a l l i of P. s t i p i t a t a l i b e r a t e t h e i r gametes only a f t e r they have been i l l um ina ted by f luorescent tubes. According to F r i t s c h (i&Q an ak inete i s a s p e c i a l i s e d type of vegetat ive reproduct ive s t ruc tu re whose c e l l wa l l i s th ickened ' to t i de over a per iod unfavourable f o r vegetat ive development 1 . In h i s op in ion , asexual reproduct ion must invo lve re juvenat ion and d i v i s i o n of the c e l l p ro top l a s t . The term "ak ine te " could be used i n t h i s study r e f e r r i n g e s s e n t i a l l y to a d i p l o i d somatic c e l l whdse protoplasm has rejuvenated and d i v ides m i t o t i c a l l y i n to 2, 4, or 8 daughter c e l l s . The coat surrounding the daughter c e l l s i s not thickened as F r i t s c h has suggested. The ak inete does not necessa r i l y serve as a r e s t i n g stage f o r P. mer id iona l i s s ince the coat breaks qu i t e e a s i l y , and the daughter c e l l s germinate in to 19 adu l t t h a l l i without any de lay . Poss ib l y t h i s i s an asexual method of x reproduct ion , s ince the protoplasm of the ak inete i s re juvenated and d i v ides i n to severa l daughter c e l l s . The akinetes found i n P. fu r fu racea have a s p e c i a l dehiscent membrane which has not been noted i n other P r a s i o l a spec i e s . The akinetes of P. s t i p i t a t a descr ibed by Friedmann (1959) are s i m i l a r to those found i n P. m e r i d i o n a l i s . 20 SUMMARY. 1. P r o v a s o l i ' s medium (conta in ing k i n e t i n , adenine, indo le a c e t i c a c i d , g i b b e r e l i n and v i tamins) brought to a pH of 8.2 - 8.4, a t temperatures of 3° - 5 °C, supports good growth of a l l stages o f development o f P r as io l a mer id iona l i s i n cu l t u r e . 2. P. mer id iona l i s i s a d i p l o-hap lo id , dimorphic p l a n t . 3. Mature d i p l o i d c e l l s a t the apex of the tha l l us d i v ide by me ios i s , each producing four hap lo id c e l l s . 4. A f t e r m i t o t i c d i v i s i o n s , the hap lo id c e l l s form the gametophytic t i s s u e which becomes a cont inuat ion of the somatic t i s sue w i th in the same t h a l l u s . 5. The gametophytic t i s sue i s poly-stromat ic and the r e s t of the t h a l l u s ( the r h i z o i d and somatic t i s sues ) i s mono-stromatic. 6. Patches o f deep green c e l l s , conta in ing p o t e n t i a l macro-gametes, a l t e rna te with patches of c e l l s o f very l i g h t colour which produce micro-gametes. Hence a mosaic pat tern i s formed a t the apex o f the t h a l l u s . 7. Sexual reproduct ion i s oogamous. The female i s sphe r i c a l and has no f l a g e l l a ; but the male gamete, which i s smal ler i n s i z e , has two f l a g e l l a a t the an te r i o r end. 8. S ix teen chromosomes were counted i n the d i p l o i d c e l l s of P. am§gtdienalis-,- and e ight i n hap lo id c e l l s . 9. P r a s i o l a mer id iona l i s reproduces asexua l l y through germination of aplanospores. 21 BIBLIOGRAPHY. Agardh, J . G . 1822. Species algarum r i t e cognitae cum synonymis, d i f f e r e n t i i s s p e c i f i c i s et desc r ip t ion ibus s u c c i n c t i s . V o l . I, p t . I I , pp. 269 - 531 • (not seen) . 1882. T i l l Algernes systematik, Nya b i d r a g . A f d . 3. Vol . 19 . Lunds Univ . A r s sk . (not seen) B o r z i , A . 1895. S tud i a l g o l o g i c i . Fasc . 2 pp. 121 - 378. (not seen) Clapper, R.S. i960. G lossary o f Genetics and other B i o l o g i c a l Terms. Vantage Press . New York. Dar l i ng ton , C D . and La Cour, L .F . i960. The Handling of Chromosomes. George A l l e n and Unwin. Lond. De Ton i , G.B. 1889. Sy l loge Algarum, V o l . I. Chlorophyceae Drew, K. 1948. Genetics and a lgae l i f e h i s t o r i e s . Nature 161 : 223/ . 1955. L i f e h i s t o r i e s i n a lgae . B i o l . Rev. 30: 343 - 390. , and Friedmann, I. 1957. Occurrence o f mot i le gametes i n P r a s i o l a . Nature 180: 557 - 8. Friedmann, I. 1959. S t ruc ture , l i f e h i s t o r y and sex determinat ion o f P. s t i p i t a t a . Ann. Bot. 23: 571 - 59^. , and Manton, I, i960. Gametes, f e r t i l i s a t i o n and zygote development i n P. s t i p i t a t a . Nova Hedwigia 1: 333 - 344. F r i t s c h , F .E . 1935* S t ructure and Reproduction of A lgae . V o l . I. Cambridge. . 1954. Rapports et communications parvenus avant l e congres a l a s e c t i on 17 (p. 83), VI I I Cong. >Int. Bo t . , Par is 22 Fujiyama, T. 1949. On the asexual reproduction and the development of Prasiola (Ag.) Menegh. i n Japan. Bot. Mag..Tokyo, 62 (729-30), 57 - 61. . 1955« L i f e h i s t o r y of P. japonica. J. Fac. Fisheries Hiroshima Univ. Vol. I, No. 1. Gay, F. 1888. Sur les Ulothrlx aeriens. B u l l . Soc. Bot. France 35*67-74. Jessen, C.F.G. 1848. PrasiOlae generis algarum monographia. (not seen) Knebel, G. 1936. Monographie der Algenreihe der P r a s i o l a l e s , insbesondere von Prasiola crispa. Hedwigia, 75i 1 - 120. Lagerheim, G. 1892. Uber die Fortpflanzung von Prasiola (Ag.) Menegh. Ber. dtsch. Bot. Tidskr. Ges., 10, 366 - 74. Lewin, R.A. 1955. Culture of P. s t i p i t a t a . Can. J. Bot. 33(1): 5 6 16. Meneghini, G. 1838. Cenni s u l l a organografia e f i s i o l o g i a d e l l e alghe. Nuovi saggi d e l l 1 I.R. Acad, d i s c i . , l e t t e r e ed a r t i , Vol. 4, p.324. Padova. (not seen) Newton, L. 1931. Handbook of B r i t i s h Seaweed. Br. Museum (Nat. H i s t . ) , Lond. Pringsheim, E.C. 1946. Pure Culturesri of Algae, Cambridge. Provasoli, L. 1958. Effect of hormones on Ulva B i o l . B u l l . 114(3): 375 - 384. Setc h e l l , W.A. and Gardner, N.L. 1903. Marine algae of P a c i f i c Coast. Univ. Cal. Publ. Bot. 1: 165 - 418. , and . 1920.Marine algae of P a c i f i c Coast. Univ. Cal. Publ. Bot. 7:291 ; 8(2): 139 - 375. Smith, G.M. 1950. The Freshwater Algae of the United States. 2nd. ed. McGraw - H i l l , N.Y. • 1955. Cryptogamic Botany. Vol . 1 . McGraw - H i l l , N.Y. 23 Storvel, R.E. 1954. Feulgen reaction. Stain Technology. Vol. 26: 35. Suhr, J.N. 1831. Beschreibung einiger neuen Algen. Flora XIV.pp.6?3-87. 709-20, 725-36 (Obtained from Royal Society Catalogue of S c i . Papers). Uda, S. 1948. Studies on the l i f e h istory of Prasiola .japonica Yatabe (Japanese with English summary). J.Jap.Bot.,22, 33-37 and 90-94-. W i l l e , N. I897. Om Farveremes Fersk van algernei. Botaniska Not. Lund. P. 31. • 1901. Studien ueber Chlorophyceen I-VII. Medd. B i o l . Station Drobak No.2 Vidensk. S k r i f t e r . I Math, naturv. Klase, 1900. no.6. Christiana. _____ • 1906. Algologische Untersuchungen an der biologischen Station i n Drontheim I-VII Det Kgl. Norske Vidensk.Selk. S k r i f t e r , no. 3. Yabe, Y. -1932. Sexual reproduction of P. japonica. S c i . Rep. Tokyo Sect. B1 : 39 - 40. Yatabe, Y.- 1891. On Prasiola .iaoonica Yatabe. Bo$. Mag. Tokyo 5:187-9. Yuasa, A. 1940. Pyrenoid-division i n P. japonica Yatabe. Bot. Mag. Tokyo 54: 196-8. 24 TABLE I. - CHROMOSOME NUMBERS IN PRASIOLA d i p l o i d hap lo id reference P. .japonica - 3 Fujiyama 1955 P. s t i p i t a t a 12 6 Friedmann 1959 P. mer id iona l i s 16 8 Ak in tob i 1961 25 ABBREVIATIONS. ak ak inete (asexual c e l l s ) ap aplanospore b blade c chromosome(s) 3h chromatophore cp c e l l p la te cw inner coat or i n d i v i d u a l c e l l wa l l f f l a g e l l a gt gametophytic t i s sue mag macro-gamete raig micro-gamete n nucleus n l nucleolus oc outer coat P pyrenoid r r h i z o i d s s t i pe s t somatic t i s sue z zygote 26 Figure 1. Culture of Prasiola meridionalis i n petri dish, x£/3. Figure 2, An adult P. meridionalis thallus. Note rhizoid, somatic tissue and gametophytic tissue, x20. FIGS. 1 & 2 - PRASIOLA MERIDIONALIS THALLI 28 :G.3 - ALTERNATION OF GENERATIONS IN PRASIOLA MBRIDIQ] *M C R O S C O P I C 6AMET0PHYTIC (HAPLOID) PHASE SPOROPHYTIC (DIPLOID) PHASE M A C R O S C O P I C 29 FIG A . LIFE CYCLE OF PRASIOLA MERIDIONALIS. Macro-gamete (haploid) (no f l a g e l l a ) d i f f e r e n t i a t i o n mitosis Micro-gamete (haploid) ( b i - f l a g e l l a t e ) d i f f e r e n I Aplanospores ^ (diploid) Syngamy (oogamy) Zygote (diploid) I mitosis J^.Adult t h a l l u s : (a) r h i z o i d (diploid) (b) somatic or sporophytic tissue | (diploid) meiosis ;iation I. Haploid c e l l s mitosis (c) Gamaiophytic tissue (haploid) (c-j) Macro-gametophytic tissue (haploid) ( C 2T Micro-gametophytic tissue (haploid) 30 Figures 5 -.10. Morphology of Prasiola meridionalis Fig. 5 Surface view of the thallus of P. meridionalis. Note the rhizoid and blade. x5 Fig. 6 Whole thallus of P. meridionalis. Note the forked rhizoid. The gametophytic tissue with very ligh t and dark areas is evident at the apex. x25 Fig. 7 Surface view of the f l a t rhizoid, short stipe, somatic tissue, and the mucilaginous material secreted by the basal c e l l s . A common coat covers the thallus. The cells of the young thallus are shaped and arranged irregularly. X1800 Fig. 8 The cells of the somatic tissue. Note the asexual cells within the center of the thallus. x1500 Fig. 9 Mature cells of somatic tissue. Dark spots in the cells are lobes of chromatophores. x850 Fig. 10 Camera lucida drawing of a young thallus showing patches formed by the gametophytic tissue. The dark patches contain cells which differentiate into macro-gametes, and the l i g h t ones, micro-gametes. x25 FIGS. 5-10. MORPHOLOGY OF i-RASIOLA MERIDIONALIS 32 Figures 11 - 16. Cytology of P ras io l a mer id iona l i s F i g . 11 Typ i c a l c e l l s of sporophyt lc t i s sue o f P. m e r i d i o n a l i s . Note the r e l a t i v e pos i t i ons of the nucleus and pyreno id . X1800 F i g . 12 Drawing of m i to t i c anaphase. S ixteen chromosomes are present a t each po l e . X1800 F i g . 13 D i v i s i o n of both nucleus and pyreno id . X1800 F i g . 14 Camera l u c i d a drawing o f f i g . 13. x2300 Sixteen chromosomes are evident a t each pole of the c e l l with the c e l l p l a te i n between. F i g . 15 Camera l u c i d a drawing of m i to t i c prophase i n c e l l s from the gametophytic t i s s u e . E ight chromosomes are loca ted c lose to the per iphery o f the nuclear membrane. X1800 F i g . 16 Camera l u c i d a drawing of m i t o t i c anaphase i n a c e l l o f the gametophytic t i s sue^ . Note e ight chromosomes moving towards each pole of the elongated c e l l . X1800 1 1 - 1 6 . CYTOLOGY OF HtASIOLA M_RILION*LIS 34 Figures 17 & 18. Gametes of P r as io l a me r i d i ona l i s . F i g . 17 Gametes escaping from ruptured gametangia. Note the micro-gamete on the r i g h t and the macro-gamete a t the top center o f the photograph. x2800 F i g . 18 Male gamete with two f l a g e l l a . x4300 FIGS. 17 & 18. GAMETES OF PRASIOLA MERIDIONALIS IS 36 Figures 19 - 23. Stages i n the l i f e cyc le of P r a s i o l a mer id iona l i s F i g . 19 Fusion o f l a rge r macro-gamete and smal ler micro-gametes^ Pr inted from a 16 mm. c ine frame. X1800 F i g . 20 Incomplete m i t o t i c d i v i s i o n of the zygote showing separate chromatophores. X1800 F i g . 21 A un i se r i a t e f i l ament r e s u l t i n g from m i t o t i c d i v i s i o n s of the zygote i n one p lane . C e l l p la tes are v i s i b l e . 1800 F i g . 22 Young t h a l l u s . Note that basa l c e l l s have formed a r h i z o i d and the common outer coat covers the whole t h a l l u s . X1800 F i g . 23 Thal lus p i c tu red i n f i g . 22, 16 days o l d e r . The r h i z o i d has become fo rked . The outer coat i s present but shows f a i n t l y . X1800 , 1 9 - 2 3 . S1*G_3 IN lHi. LIFE CYCLh OF tnAoICLA KJ^UU*US 38 Figures 24 - 28. Stages of growth of P r a s i o l a mer id iona l i s and asexual reproduct ion . F i g . 24 Young tha l lus - 12 weeks o l d . Note the common coat . x500 F i g . 25 Adu l t t ha l l u s with mucilaginous mate r i a l a t the base o f the r h i z o i d . x500 F i g . 26 M i t o t i c d i v i s i o n o f the mature d i p l o i d c e l l , forming aplanospores. At t h i s stage the four chromatophores are incomplete ly pa r t i t i oned by the c e l l p l a t e s . x2800 F i g . 27 An advanced stage o f f i g . 26. Each aplanospore (w i th in the mother c e l l coat)has a pyreno id , nucleus and a t h i n c e l l w a l l . x2100 F i g . 28 Four, s i x , or e ight aplanospores w i th in a common coat . x1500 FIGS. 2 4 - 2 8 . STAGES OF GROWTH OF PRASIOLA MERIDIONALIS AND ASEXUAL REPRODUCTION. 28 PIG.3 - ALTERNATION OF GENERATIONS IN PRASIOLA MERIDIONALIS. M I C R O S C O P I C GAMETOPHYTIC (HAPLOID) PHASE SPOROPHYTIC (DIPLOID) PHASE M A C R O S C O P I C 29 FIG .4. LIFE CYCLE OF PRASIOLA MERIDIONALIS. Macro-gamete (haploid) (no f l a g e l l a ) d i f f e r ent ia t i o n mi tos i s I Micro-gamete (haploid) ( b i - f l a g e l l a t e ) Syngamy (oogamy) Zygote ( d ip lo id ) I mitos i s i d i f f e r e n t i a t i o n ^ A d u l t t h a l l u s : (a) r h i z o i d (d ip lo id ) (b) somatic or sporophyt ic t i s sue I ( d i p l o id ) Aplanospores ( d ip l o id ) meiosis i . Haplo id c e l l s MI t o s i s (c) Gametophytie t i s sue (haploid) (c-|) Macro-gametophytic t i s s u e (haploid) (egJ Micro-gametophytic t i s sue (haploid) 

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