HOW TO KNOW THE FRESH-WATER ALGAE 



and centrally located; food reserve in the form of an insoluble starch- 

 like substance, paramylum which is negative to the starch test with 

 iodine, and fatty substances; cell membrane in the form of a pellicle, 

 rigid or plastic, frequently striated; sexual reproduction unknown. 



5 Cryptophyta (Cryptophyceae of some authors). 



Cells solitary or colonial; mostly swimming by means of 2, often 

 laterally placed or sub-apical flagella; chromatophores large and 

 brown, or rarely blue, often with pyrenoids; food reserve in the form 

 of starch or oil; membrane firm but relatively thin; sexual reproduc- 

 tion unkown. 



6 Pyrrhophyta. (Dinoflagellates). 



Cells solitary or (rarely) filamentous; mostly swimming by means 

 of 2 flagella, one commonly wound about the cell in a transverse 

 furrow, and one extended posteriorly from the point of flagellar at- 

 tachment in a longitudinal furrow; cells dorsiventrally flattened and 

 differentiated, the longitudinal furrow extending along the ventral 

 surface; cell wall, if present, firm and often composed of regularly 

 arranged polygonal plates (as in the so-called armored or thecate 

 Dinoflagellates); pigments chlorophyll, carotene, four xanthophylls, 

 brown phycopyrrin, red peridinin (the latter sometimes predominating) 

 contained within chromatophores; food reserve starch or a starch-like 

 substance, and oil; a pigment (eye) spot often present; sexual repro- 

 duction unknown. 



7 Rhodophyta. (Red Algae). 



Plants simple or branched filaments (unicellular in one question- 

 able form); pigments contained within chromatophores, are chloro- 

 phyll, xanthophyll, carotene, phycocyanin and phycoerythrin, in the 

 freshwater forms appearing blue-green, gray-green, or violet (not red); 

 food reserve in the form of a special starch (floridean) which is nega- 

 tive to the iodine test for starch; walls relatively thick and often 

 mucilaginous, sometimes furnished with pores through which proto- 

 plasmic extensions occur; sexual reproduction by heterogametes, but 

 the male elements drifting and not swimming; thalli often of macro- 

 scopic size. 



8 Chloromonadophyta (Chloromonads). 



An obscure and little-understood group composed of but a few 

 genera and species; cells swimming, flagella one or two, apically at- 

 tached; chromatophores green, with chlorophyll (supposedly) predomi- 

 nating, but with an abundance of xanthophyll also present; food re- 

 serve in the form of oils or a fat; contractile vacuoles and a reservoir 

 in the anterior end of the cell; cell contents with trichocysts radiately 

 arranged just within the cell membrane (in the genus Gonyostomum), 

 sexual reproduction unknown. 



8 



