146 THE VARIOUS FORMS OF PLANTS 



ever, contain chlorophyll. In the red and brown seaweeds the chloro- 

 phyll is concealed by other coloring material in the plant body. In the 

 olive-brown fucus (the common rockweed) it is easy ^to prove the presence 

 of chlorophyll by cutting open the bladders which are found in the plant 

 body. The red seaweeds are among the most beautiful and delicate of 

 all plants. They may be mounted under water upon cardboard and 

 then studied after drying. 



Rockweed, a brown alga, showing the distribution on rocks below high-water mark. 



Green Algae. The plants known as the green algae are of more 

 interest to us because of their distribution in fresh water, and 

 also because of their economic importance as a supply of oxygen 

 for fish and other animals in the waters of our inland lakes and 

 rivers. Our attention is called to them in an unpleasant way at 

 times, when, after multiplying very rapidly during the hot summer, 

 they die rapidly in the early fall and leave their remains in our 

 water supply. Much of the unpleasant taste and odor of drinking 

 water comes from this cause. 



Pond Scum (Spirogyra). This alga is well known to every 

 boy or girl who has ever seen a small pond or sluggish stream. It 

 grows as a slimy mass of green threads or filaments. Frequently 

 it is so plentiful as almost to cover the surface of the water, buoyed 



