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; M, 

 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-muJ;ile 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 //, 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 si.xteen individuals 



enclosed in a thin gelatinous mem- 

 brane. Kach cell possesses two cilia 

 for flagella), which e.xtend 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, which 

 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). 

 p- jg Eudorina elegans is somewhat similar, 



Pandorina morum (Mull.) Bory. I, but -when the gametes are formed cer- 



Tnotile colony; II, colony divided into . - ., n, ,i,-,.;j^ :„+.^ ^..-^-toor^ 



16 daughter colonies; III, sexual colony, tain mother cells divide into sixteen 



gametes escaping; IV, V, conjugating jniall motile males or sperms, and 



gametes; VI, VII, young and old zvgu- j. . i 



spore; VIII. zygospore forming a large certain other mother cells divide into 



swarm spore, which is free in IX; X, . , , ,-i f i ^,. ^^^^ 



same large swarm spore divided to form -Sixteen large motile females or eggs. 



young colony. (After Pringsheim.) 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. 



