VEGETATION TYPES AND STRUCTURES. 467 



ditions than we are with the classification of plants according 

 to natural relationships. Plants may have the same vegetation 

 type, grow side by side, and still belong to very different floristic 

 types. For example, the cactus, yucca, three-leaved sumac, 

 the sage-brush, etc., have all the same general vegetation type 

 and thrive in desert regions. The red oaks, the elms, many 

 goldenrods, trillium, etc., have the same general vegetation type, 

 but represent very different floristic types. The latter plants 

 grow in regions with abundant rainfall throughout the year, 

 where the growing season is not very short and temperature 

 conditions are moderate. Some goldenrods grow in very sandy 

 soil which dries out quickly. These have fleshy or succulent 

 leaves for storing water, and while they are of the same floristic 

 type as goldenrods growing in other places, the vegetation type 

 is very different. The types of vegetation which fit plants for 

 growing in special regions or under special conditions, they have 

 taken on in response to the influence of the conditions of their envi- 

 ronment. While we find all gradations between the different types 

 of vegetation, looking at the vegetation in a broad way, several 

 types are recognized which were proposed by Warming as follows: 



905. Mesophytes. These are represented by land plants 

 under temperate or moderate climatic and soil conditions. The 

 normal land vegetation of our temperate region is composed 

 of mesophytes, that is. the plants have mesophytic structures 

 during the growing season. The deciduous forests or thickets 

 of trees and shrubs with their undergrowth, the meadows, pas- 

 tures, prairies, weeds, etc., are examples. In those portions 

 of the tropics where rainfall is great the vegetation is mesophytic 

 the year around. 



906. Xerophytes. These are plants which are provided with 

 structures which enable them to live under severe conditions 

 of dryness, where the air and soil are very dry, as in deserts or 

 semideserts, or where the soil is very dry or not retentive of 

 moisture, as in very sandy soil which is above ground water, or 

 in rocky areas. Since the plants cannot obtain much water 

 from the soil they must be provided with structures which will 



