PLANT SOCIETIES 



319 



transpiration during the summer (or in regions like South- 

 ern California in the rainy season) and a greatly reduced 

 surface during the winter (or the dry season). 



In the case of trees the reduction of surface is brought 

 about by the fall of the leaves (Sect. 186), and in the case 

 of herbaceous perennials it is secured by the death of the 

 green stem and the leaves, so that only a compact root, 

 rootstock, or bulb is left alive underground. That is to 

 say, the perishable or annual part of tropophytes has the 

 characteristics of mesophytes or even of moisture-loving 

 plants, while the perennial part is constructed on the plan 

 of xerophytes. 



391. Halophytes. — A halophyte is a plant which can 

 thrive in a soil containing much common salt or other 

 saline substances. The seaside obviously occurs to one as 

 the region of halo- 

 phytic vegetation, 

 but many inland 

 areas contain halo- 

 phytic plants, for 

 instance the neigh- 

 borhoods about salt 

 springs and the 

 " alkali " lands of 

 the southwest and 

 the Pacific Slope. 

 The presence of salt i 

 in the soil renders 

 absorption of the 

 soil-water comparatively difficult, since osmosis takes place 

 more readily between ordinary water and the liquid 



I'm. 226. — The Mangrove, a Halophytio Tree of 

 Southern Florida and the Tropics. 



