VEGETATION TYPES. 483 



per, will be presented here. These vegetation types are classified 

 into societies as follows: 



I. Warming's Vegetation Types. 



943. Mesophytes. These are represented by land plants 

 under temperate or medium climatic and soil conditions. The 

 north temperate regions (with the exception of mountain heights, 

 the arid regions, the sand-dune areas, etc.) are most favorable 

 for the development of the mesophyte type. The normal land 

 vegetation of our temperate region is composed of mesophytes; 

 example, the deciduous forests or thickets of trees and shrubs 

 with their undergrowth, the meadows, pastures, and prairies. 

 Mesophytes occur, however, in arctic regions; for example, the 

 low-growing mats of grass, or herbaceous vegetation which 

 appears during the summer months. The rainy-season flora of 

 the deserts or plains also forms mesophytic societies. The land 

 of these regions, however, is not populated by mesophytes alone. 

 There are many xerophytic plants growing in mesophytic soci- 

 eties; for example, the conifers in the "mixed" forests are xero- 

 phytes, and make the characteristic xerophytic society of sub- 

 arctic or subalpine regions. There are many other examples of 

 xerophytic plants growing in mesophytic societies, as the purslane 

 (Portulaca), the stonecrops (Sedum), some of the cacti, etc. 



944. Xerophytes. Plants growing in very dry regions, or 

 under conditions of environment where absorption of water by 

 the roots is difficult, or such as to favor the loss of water from 

 the aerial organs in excessive amounts for long periods, are 

 known as xerophytes. A plant having a habit or structure 

 which fits it to live under these extreme conditions is a xerophyte. 

 The most characteristic xerophytic plants are the perennials 

 which inhabit the desert. Less highly specialized xerophytes 

 are those which grow in subarctic or alpine regions, or in rocky 

 places or on sand-dunes. In the deserts especially, xerophytic 

 plants are developed to the exclusion of others, except in certain 

 specially favored localities, and excepting also the rainy-season 



