34 



NATURAL HISTORY OF THE FARM 



THE PLANT LIFE OF THE STREAM 



The rapids 

 are by no means 

 destitute of life. 

 Given natural 

 waters, a tem- 

 perature above 

 freezing, light 

 and air, plants 

 will grow any- 

 where: here, 

 they must be 

 such plants as 

 can withstand 

 the shower of 

 stones that every 

 flood brings 

 down upon them. 

 They must be 

 simply organized plants, that are not killed when their cell 

 masses are broken asunder. Such plants are the algae; and 

 these abound in the swiftest waters. They form a thin 

 stratum of vegetation covering the surfaces of rocks and tim- 

 bers. Its prevailing color is brown, not green. Its dominant 

 plants are diatoms. These form a soft, gelatinous, and very 

 slippery coating over the stones. Individually they are too 

 small to be recognized without a microscope, but collec- 

 tively, by reason of their nutritive value and their rapid 

 rate of increase, they constitute the fundamental forage 

 supply for a host of animals dwelling in the stream, bed with 

 them. 



There are green algae also in the rapids. The most con- 

 spicuous of these is Cladophora, which grows in soft trailing 

 masses of microscopic filaments, fringing the edges of stones in 



Fig. 12. Spray of riverweed (Potamogelon crispus). 

 From a drawing by Miss Emmeline Moore. 



