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INTRODUCTION TO CYTOLOGY 



features associated with this fusion are more varied in plants than in 

 animals. This is especially true of the algae and fungi. 



Algae. — In Ulothrix fertilization consists in the complete union of 

 two morphologically similar, motile biciliate gametes (Fig. 114, A). 

 In Fucus the two gametes are very dissimilar : the male (spermatozoid) is 

 small, laterally biciliate, and actively motile (Fig. 114, B), while the 

 female (egg), though discharged from the oogonium, is large and passive, 

 as in all higher plants and animals. In (Edogonium (Fig. 114, D, E) the 



Fig. 114. — Spermatozoids of plants. 



A, Ulothrix: 1, gamete; 2, gametes fusing (isogamy) ; 3, zygospore. B, Fucus. {After 

 Guignard.) C, Zamia. (After Webber.) D, bit of filament of (Edogonium; spermatozoids 

 escaping from antheridial cells below; spermatozoid about to enter egg above. {After 

 Coulter.) E, spermatozoid of (Edogonium. F, Chara. (After Belajeff.) G, Onoclea. 

 (After Steil.) For figures of spermatozoids of Blasia, Polytrichum, Equisetum, and Marsilia, 

 see Figs. 28, 29, 30, and 32. 



egg is not shed from the cell which produces it, but is fertilized in situ, 

 a condition which is retained in all the higher plant groups. The sperm- 

 atozoid in this genus has a crown-like ring of cilia. In Spirogyra (and 

 other Conjugatae) certain vegetative cells, without further morphological 

 differentiation, function as gametes. The entire contents of such a cell 

 pass through a conjugation tube to a similar cell in an adjacent filament, 

 where the two unite to form the zygospore. The two nuclei fuse, but the 

 chloroplasts furnished by the contributing '(" male") gamete may event- 

 ually degenerate (Zygnema). In Polysiphoiiia a non-motile male gamete 



