THALLOFHYTA: ALGAE 



71 



rangia in crowded clusters. Each sporangium has a one-celled stalk and 

 produces 8, 16, or 32 laterally biciliate zoospores (Fig. 57F). At first 

 the sporangium has a single nucleus, the first two divisions of which 

 result in a reduction of chromosomes. After three, four, or five simul- 

 taneous free-nuclear divisions have occurred, uninucleate protoplasts are 



Fig. 57. Cidleria muUifida. A, gametophyte, one-third natural size; B, male gametan- 

 gium, X600; C, two female gametangia, X600; D, an egg and a sperm in the living condi- 

 tion; E, voung sporophyte 30 days after fertilization; F, two nearly ripe sporangia, XGOO; 

 G, a zoospore in the living condition. {A, after Thuret; D, E, G, after Yamanouchi.) 



formed by cleavage of the cytoplasm. Thus the zoospores are haploid 

 (Fig. blG). 



The gametophytes, which are produced by the zoospores, are either 

 male or female but are ahke vegetatively (Fig. 57.4). They are erect, 

 ribbon-like, and dichotomously branched, reaching a length of about 20 

 cm. They are several layers of cells in thickness. The male and female 

 gametangia, which are somewhat similar in appearance, are borne in 



