HOW TO KNOW THE FRESH- WATER ALGAE 



being used for the assay and detection of biologicals (vitamins and 

 growth-promoting or growth-inhibiting substances) in tissue culture 

 work. Some of the research on cancer involves studies in the physi- 

 ology and reproduction of algal cells. I 



Whatever the interests in freshwater algae may be, the student a 

 who has access to a microscope can find many hours of fascination 

 in a few drops of pond watei. 



The term "algae," derived from the Latin name for sea-wrack, 

 has come to be applied to all relatively simple marine and fresh- < 

 water vegetation. Actually, of course, many different kinds of organ- 

 isms are included among the plants which lie outside or below the 

 realm of mosses (Bryophytes), the ferns (Pteridophytes), and the seed- 



bearing plants (Spermatophytes). Included under "algae" are the 

 smallest and most simple of chlorophyll-bearing organisms, the entire 

 plant being but a single cell. Some of these may be less than 1 micron 

 in diameter. At the other extreme, some of the brown algae (Phaeo- 

 phyta) include the longest plants, in the world. One of the kelps (Macro- 

 cystis) of the Pacific Ocean, for example, may reach 700 feet, and even 

 greater lengths have been claimed. 



The student soon learns that "algae" include several divisions 

 or phyla of the plant kingdom, and that there are incorporated even 

 some groups of organisms, which, strictly speaking, belong neither 

 to the plant nor to the animal kingdom (Euglenaceae, Dinoflagellatae, 

 and many of the yellow green algae such as Synura and Dinobryon). 

 These are forms which usually are treated as chlorophyll-bearing 

 protozoa in a reference book dealing with one-celled animals. Sev- 

 eral of the swimming, protozoan-like forms have definitely plant-like, 

 non-motile relatives, however, which more than justify their being given 

 a place among the algae. 



The reader who is not familiar with the classification of plants and 

 animals, and with the terminology used for the different categories 

 may wish to refer to the following definitions. 



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