CEDOGONIEJE. 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- 

 Tided 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 grow into an ordinary filament in exactly 

 the same manner as the zoospores. 



(a) It will be unnecessary in 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. 



