CHAPTER XXIX 

 PLAN! SOCIETIES 



357. WHAT PLANT SOCIETIES ARE.— In the long course 

 of evolution, in which plants have been accommodating 

 themselves to the varying conditions in which they are 

 obliged to grow, plants have become adapted to erenj 

 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 as 

 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 chiefl}' with the moisture su])ply. 

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

 comprising aquatic and bog vegetation (Fig. 3G9) ; (2) 

 xerophytic or arid-region societies, comprising desert and 

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

 or mid-region societies, comprising the vegetation in 

 intermediate regions (Fig. 370). Mesophytic vegetation 

 is characteristic of most regions which are fitted for 

 agriculture. The halophytic or salt-loving societies are 

 also distinguished, comprising the seashore and salt -area 

 vegetation (Fig. 371). Much of the characteristic 

 scenery of any place is due to its plant societies (337). 

 Xerophytic plants usually have small and hard leaves, 

 appai-ently to prevent too rapid transpiration. Usually, 

 also, they are characterized by stiff growth, hairy cover- 

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



(219) 



