No. IO.] FRESH- WATER ALG.E. 73 



Key to Genera. 



i. With clustered tufts of branches. .. .Batrachospermum* 

 Without clustered tufts 2 



2. Thallus three to seven mm. in length Chantransia 



Thallus thirty to sixty cm. in length Thorea 



Description of Genera. 



Batrachospermum Roth. A wholly fresh-water genus. 

 The plants are dioecious, of a violet or bluish green color. Thal- 

 lus is from sixteen to twenty cm. in length, moniliform, gela- 

 tinous, slippery, consisting of an axile series of cells growing by 

 means of a hemispherical apical cell, and an accessory parallel 

 series, covered with clustered tufts of branches which are more 

 or less scattered. The carpogonium grows in a cell at the 

 extremity of a short branch which stands out directly from the 

 main branch; it possesses a short, straight trichogyne, and 

 after fertilization develops a dense mass of exposed carpo- 

 spores. 



B. vagum (Roth) Ag., Fig. 278. 



\B. anatinum Sirdt. ; B. Boryannm Sirdt. ; B. Corbula 

 Sirdt. ; B. ectocarpnm Sirdt. ; B. moniliforme var. typicum, 

 and var. chlorosum Sirdt. ; B. pyramidale Sirdt. ; B. virga- 

 tum Sirdt.] 



Chantransia Fries. Dioecious, red, steel-blue, or purp- 

 lish violet, growing in fresh and salt water. Filaments articu- 

 late, branched ; branches simple or compound ; mucilage 

 lacking. 



The carpogonium develops, after fertilization, numerous 

 gonimoblasts in small clusters, upwards and on one side. 

 Asexual multiplication by tetraspores developed on ends of 

 cells. 



Thorea Bory. This genus possesses but one species, T. 

 ramosissima Bory. The thallus is round, filamentous, much 

 branched, the thickness of a horse hair, of a purple-brown or 

 dark brown color, very mucous, and reaching the length of 

 thirty to sixty cm. The branches are short and compact, 

 slightly attenuated, and the cells are from two to five times 

 longer than their diameter. The cells possess starch-like 

 granules, and the spores are naked and non-motile. 



