(EDOGONIEJS. 249 



themselves in the substance of the oosphere (B, z, Fig. 167). 

 After fertilization the oosphere becomes covered with a thick 

 and colored (brown or red) coat, and it then becomes an 

 oospore (C, Fig. 167). 



331. In certain cases the cells which produce the sper- 

 matozoids occur on the same filaments which produce 

 oogonia also ; this is the monoecious type. In other cases one 

 of the ordinary cells of the filament which bears oogonia be- 

 comes divided by simple fission into two or more cells ; the 

 protoplasm in each of these new cells condenses into an 

 ovate mass, which by a rupture of the cell-wall is set free as 

 a motile body resembling a small zoospore, and, like it, pro- 

 vided with a crown of vibrating cilia; this is the androspore. 

 After swimming about for some time, it comes to rest upon, 

 or near to, an oogonium, and attaches itself by root-like pro- 

 jections, exactly as in the case of the growth of true zoo- 

 spores ; the result of the growth of the androspore is the pro- 

 duction of a miniature plant composed of three or four cells 

 (A, m, m, and B, m, Fig. 167). The upper cells of these 

 little plants develop spermatozoids, and hence the plants are 

 called dwarf males. This is the so-called gynandrous type 

 (A and B, Fig. 167). In a third class of cases, the ordinary 

 plant filaments are of two kinds, the one producing sperma- 

 tozoids only, and the other only oogonia ; this is the dioecious 

 type (D, Fig. 167). 



332. After a period of rest the oospore germinates by 

 rupturing its thick coat, and permitting the escape of the 

 contents, enclosed in a thin envelope ; by this time the pro- 

 toplasm has divided into four portions, which take on an 

 oval form, and develop a crown of cilia (F, Fig. 167). They 

 soon escape from the investing membrane, and after a brief 

 period of activity groAV into an ordinary filament in exactly 

 the same manner as the zoospores. 



(a) It will be unnecessary iu this place to fully discuss the arrange- 

 ment of the genera belonging to this class ; they probably may be all 

 brought within the limits of one order coextensive with the class. 

 Wood has separated* two sub-families (= sub-orders), which differ in 



* " A Contribution to the History of the Fresh-water Algae of the 

 United States," by H. C. Wood, 1872, 



