io6 



CHLOROPHYCEAE 



bands (cf. fig. 73). At conjugation, papillae from the two cells meet 

 or else the naked amoeboid gametes fuse immediately outside the 

 cells, whilst in C. parvulum there is some evidence of sexual 

 differentiation. After the gametes have fused two of the chloro- 

 plasts degenerate and the zygospore on germination divides twice, 



Fig. 72. Closterium. A— D, C. Ehrenbergii, stages in cell division. w = nucleus, 

 5 = septum, z; = vacuole. E, C. lanceolatum, chloroplast structure. F, Closterium 

 sp. showing structure. w = nucleus. G, C. lineatum, first stage in conjugation. 

 H, C. rostratum var. brevirostratum, zygospore formation, second stage. 

 I, C. calosporum, mature z\'gospore. (A-H, after Fritsch; I, after Smith.) 



during which meiosis takes place. Two daughter cells are then 

 formed, each containing one chloroplast and two nuclei, but one of 

 the latter subsequently degenerates. The genus is wholly fresh 

 water. 



Many of the desmids are planktonic and possess modifications, 

 e.g. spines, which may be regarded as adaptations to this mode of 

 existence. The group is extremely widespread, though it is absent 



