KEY TO THE CLASSES AND THE GENERA OF THE 

 FRESH WATER ALG^E. 



CLASSES OF THE ALG^E. 

 Rosy red, blood-red, reddish-brown, purple or blackish; many 



celled ................. CLASS i. 



Chlorophyll-green, sometimes becoming crimson, purplish, flesh- 



color or yellow-brown; 1,2 or many celled; often nucleated, 



CLASS II. 



Never chlorophyll-green; colorless or variously colored; i or many 

 celled; in jelly when out of the water ...... CLASS HI. 



KEY TO THE GENERA OF THE 



CLASS I. 



T Olive, brown or grey, black with age; filamentous, often hollow, 



bristle-like, rigid (A). 

 T Violet, violet-purple or bluish-green; filaments articulate, branched 



or not (E). 



T Purple; tufts loose; filaments i in. long, not branched (D). 

 ^[ Purplish, smooth, forming a firmly attached coating to stones, 



Hildebrantia, 7 

 If" Brownish red, vermillion, or greenish with red centre; cells 4-8, 



free or in a short lived cluster ..... Chlamydococcus, 38 

 ^[ Blood red, cells large, tegument thick, lamellose, stem ringed, 



Urococcus, 66 

 A. Filaments nodose, tufted; fertile filaments hollow, with internal 



axillary thread; in rapid water (B). 

 A. Filaments transversely banded or annularly constricted; with in- 



ternal central axis (C). 



