CHAPTER VI 

 THE FRESH-WATER ALGAE 



(EXCLTZDING THE BlUE-GrEEN AlGAe) 



By JULIA W. SNOW 

 Associate Professor of Botany in Smith College, Northampton, Mass. 



The fresh-water algae are among the most widely distributed of 

 plants. They are found in all natural bodies of water, whether 

 these be rapidly-running streams, brooks, and rivers, or the more 

 quiet bodies, such as pools, ponds, and lakes. They abound where- 

 ever there is moisture. All low-growing vegetation in moist places, 

 the bark of trees, the earth itself, and even snow-covered moun- 

 tains, bear species, although they may be invisible to the naked 

 eye. 



The forms of the fresh-water algae are most varied, and there are 

 all gradations from the most minute cell of primitive, spherical 

 shape to the large filamentous, richly-branched structure, or cell 

 complex. The difference between the simple unicellular forms and 

 many of the higher forms is less than would appear at first sight. 

 The larger forms often instead of being complex organisms with 

 many organs, each with its own special function, seem to be more 

 Uke aggregates of unicellular individuals, each capable of perform- 

 ing all the life functions, and each living independently of its 

 neighbors. This is manifested in forms where a single cell is sepa- 

 rated from all others and continues to live and to reproduce. An 

 example of this is seen in Stigeoclonium and Chaetophora, which 

 under certain conditions fall apart completely, and each cell exists 

 indefinitely as a unicellular organism undergoing division in three 

 directions. Such a state is known as the pahnella condition. 

 Each cell in this aggregate, however, when in the right enviroimient, 

 has the power to reproduce again the original plant, a fact which 

 would indicate that environment as well as heredity is a factor 



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