486 RELATION TO EN VIROiX MENT- 



warm oases in arctic lands, the forested areas along river bottoms 

 in prairie or plains regions, etc. 



928. Aquatic plant societies — In general we might distinguish 

 three kinds, ist. Fresh-water plant societies, with lloating algae 

 like s])irogvra, a-dogonium, etc., the floating duck-meats, riccias; 

 the plants of the lily type with roots and stems attached to the 

 bottom and leaves floating on the surface, hke the water-hly 

 and certain pondweeds, and finally the completely submerged 

 ones hke certain pondweeds, the bassweed (Chara), etc. 

 2d. Marine plant societies, which are made up mostly of the 

 red and brown alga; or "seaweeds," though some green alga; 

 and flowering plants also occur. 3d. The salt marshes where 

 the water is brackish and there is usually a luxuriant growth of 

 marsh-grasses. 



