20 GUIDE TO CRYPTOGAMS. 



DIATOMACE^]. (Diatoms.) Cell-wall composed almost 

 entirely of silex. Sexual reproduction by zygospores. (Genera 

 not given.) 



3 c. Color grass green. 



DESMIDIACE^J. (Desmids.) Cell-wall without silex. 

 Cells usually divided into symmetrical halves b}' a deep constric- 

 tion. Sexual reproduction by zygospores. (Genera not given.) 



CHLOROPHYLLOPHYCE^]. Cell-wall without silex, 

 often more or less gelatinous. Cells often imbedded in a jelly. 

 Not constricted as in Desmidiaceae. Reproduction entirely non- 

 sexual. (Genera not given.) 



FUCACEJ1. Genera : 



1 a. Thallus composed of a icell-marked stem-like portion 

 and distinct leaf-like appendages, 



Sargassum. (Gulf-weed.) Air-bladders distinctly stalked. 

 (Occurs south of Cape Cod and in the Gulf Stream.) 

 1 b. Thallus without leaf like appendages. 



Fucus. Branches of the thallus flattened, with a midrib. 

 Receptacles terminal, continuous with the frond. Often with air- 

 bladders. 



Ascophyllum. Midrib wanting. Receptacles on special 

 lateral branches. With air-bladders. 



PH^EOSPORE^E. Genera : 

 1 a. Thallus flat and leaf like. 

 2 a. With a midrib. 

 3 a. Frond perforated with numerous holes. 



Agarum. (Sea-colander.) Frond stalked. Plant growing 

 in deep water, often washed ashore during storms. 



3 b. Frond not perforated. 



Alaria. Frond stalked, having a few ecostate laminae borne 

 like leaflets below the main lamina. 

 2 b. Without a midrib. 



4 a. Frond leathery, stalked. 



