i6o 



MORPHOLOGY. 



takes place by gametes which are of unequal size, the smaller one repre- 

 senting the sperm and the larger one the egg as in E and F. These con- 



Fig. 163. 



Chlamydomonas pulvisculus (Mull.) Ehrb. A, an old motile individual; n, 

 nucleus; p, pyrenoid; s, red eye spot; v, contractile vacuole; B, motile indi- 

 vidual has drawn in its cilia and divided into two; C, mother plant has drawn 

 in its cilia and divided into four non-motile cells; D, pamella stage; E, female 

 gamete egg; F, male gamete sperm ; G, early stage of conjugation; H, zygo- 

 spore with conjugating tube and empty male cell attached. (After Wille.) 



jugate as in G and H, the protoplasm of the smaller one passing over into 

 the larger one, and a zygospore is thus formed. 



337. Of those which form colonies, Pandorina morum is widely dis- 

 tributed and not rare. It consists of a sphere formed of sixteen individuals 



enclosed in a thin gelatinous mem- 

 brane. Each cell possesses two cilia 

 (or flagella), which extend from the 

 broader end out through the envelop- 

 ing membrane. By the movement 

 of these flagella the colony goes roll- 

 ing around in the water. When the 

 plant multiplies each individual cell 

 divides into sixteen small cells, whkh 

 then grow and form new colonies. 

 Reproduction takes place when the 

 individual cells of the young colonies 

 separate, and usually a small indi- 

 vidual unites with a larger one and 

 a zygospore is formed (see fig. 164). 

 Eudorina elegans is somewhat similar, 

 but when the gametes are formed cer- 

 tain mother cells divide into sixteen 

 small motile males or sperms, and 

 certain other mother cells divide into 

 sixteen large motile females or eggs. 

 These separate from the colonies, and 

 the sperms pair with the eggs and fuse to form zygospores. This plant as 

 well as Chlamydomonas pulvisculus foreshadows the early differentiation of 

 sex in plants. 



Fig. 164. 



Pandorina morum (Mull.) Bory. I, 

 motile colony; II, colony divided into 

 16 daughter colonies; III, sexual colony, 

 gametes escaping; IV, V, conjugating 

 gametes; VI, VII, young and old zygo- 

 spore; VIII. zygospore forming a large 

 swarm spore, which is free in IX; X, 

 same large swarm spore divided to form 

 young colony. (After Pringsheim.) 



