242 



ECOLOGY 



Halophytes, "salt plants," is a term used to designate a 

 fourth class, based not directly upon the water factor, but 

 upon the presence of a particular mineral in the water or 

 the soil, which they can tolerate. They seem to bear a 

 sort of double relation to hydrophytes on the one hand and 

 to xerophytes on the other. 



349. Hydrophyte Societies. — These embrace a number 

 of forms, from those inhabiting swamps and wet moors to 

 the submerged vegetation of lakes and rivers. An exami- 



464. — A hydrophyte society of floating pond- 

 weed. 



465. — A water plant (Sagit- 

 taria naians), showing the 

 slender, ribbonlike, submerged 

 leaves, the broad, rounded, 

 floating ones, and the very 

 slightly developed root system. 



nation of almost any kind of water 

 plant will show some of the phy- 

 siological effects of unlimited 

 moisture. Take a piece of pondweed, or other immersed 

 plant out of the water and notice how completely it col- 

 lapses. This is because, being buoyed up by the water, 

 it has no need to spend its energies in developing woody 

 tissue. Floating and swimming plants will generally be 

 found to have no root system, or only very small ones, 



