ii8 



THE ALGAE 



plants. The cells, which have a cellulose membrane, contain dis- 

 coid chloroplasts without any pyrenoids together with one nucleus. 

 Cytoplasmic streaming is very readily observed, especially in the 



Fig. 68 Charales. A, B, stages in development of antheridium of 

 Chara. 1-3, segments and cells to which they give rise. C, section of 

 almost mature antheridium of Nitellaflexilis. b = flask cell, c = extra 

 basal cell. D, C. tomentosUi single plate with manubrium and 

 spermatogenous threads. E, C. tomentosa, apex of manubrium with 

 spermatogenous threads, a = primary head cell, b = secondary head 

 cell. F-I, C. foetida, stages in formation of antherozoids in sper- 

 matogenous threads. J, mature antherozoid. (A, B, after Goebelj 

 C-E, J, after Grove ; F-I, after Fritsch.) 



internodal cells. Sexual reproduction is by means of a character- 

 istic oogamy where Ught intensity plays a part in determining the 

 production of the sex organs. The species are either dioecious or 

 monoecious, in which latter case the oogonia and antheridia are 

 juxtaposed, the oogonia being directed upwards and the antheridia 

 downwards, both organs usually appearing on secondary lateral 

 branches of limited growth. 



