CHAPTEB XXIX 

 PLANT SOCIETIES 



357. WHAT PLANT SOCIETIES ARE. In the Long COUrse 



of evolution, in which plants have been accommodating 

 themselves t<> the varying conditions in which they are 

 obliged 1" grow, plants havt becotm adapted to every 

 different environment. Certain plants, therefore, may live 

 together or near each other, all enjoying the same con- 

 ditions and surroundings. These aggregations of plants 

 which are adapted to similar conditions are known ;is 

 plant societies. 



358. Moisture and temperature are the leading factors 

 in determining plant societies. The great geographical 

 societies or aggregations of the plant world are for con- 

 venience associated chiefly with the moisture supply. 

 These are: (1) hydrophytic or wet-region societies. 

 comprising aquatic and bog vegetation (Fig. 369); (2) 

 xerophytic <>r arid-region societies, comprising deserl and 

 mosl sand-region vegetation (Fig. 344); (3) mesophytic 

 or mid-region societies, comprising the vegetation in 

 intermediate regions (Fig. 370) Mesophytic vegetation 

 j v characteristic of mosl regions \\lii--li are fitted for 

 agriculture. The halophytic or Bait-loving Bocietiea are 

 also distinguished, comprising the Beashore and salt-area 

 vegetation (Fig. 371). Much of tli>' characteristic 

 scenen of anj place is due to it- plant societies (337). 

 Xerophytic plants usuallj have small and hard leaves, 

 apparently to prevenl too rapid transpiration. I sually, 

 also thej are characterized bj Btiff growth, hairj cover- 

 ing spines, or a much -contracted plant-body, and often 



