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 
Fic. 12. Spray of riverweed (Potamogeton crispus). 
From a drawing by Miss Emmeline Moore. downupon 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 isbrown,not green. Itsdominant 
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 algze 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 stonesin 
