MODIFICATIONS OF FOKM 



209 



vegetation is actually submerged, the plants specially developed under 

 such conditions arc termed Hydrophytes. Where the water is 

 brackish or salt, plants assume the characters of Halophytes. But 

 where the conditions as regards temperature and water-supply are 

 not extreme, though there may be marked seasons, the vegetation 

 would be described as consisting of Mesophytes. Such groupings 

 cannot be drawn with definiteness. They must be held as generally 

 descriptive rather than mutually exclusive. In point of fact the 



Fig. 141. 

 Succulent stem and flowers of a Cactus. (After Figuier.) 



communities overlap and graduate one into another. Naturally 

 the distinctive characters impressed upon each community are best 

 illustrated by extreme types. 



Xerophyte Vegetation is characterised by various features which 

 nave the effect, individually or collectively, of controlling transpira- 

 tion, and thus making the best of a limited water-supply. The leaf- 

 area is reduced, and its texture is often fleshy, so as to serve for 

 water-storage, as in the Stonecrop, Aloe, or Onion. In other cases 

 leaf-reduction may go along with a corresponding distension of the 

 stem, which becomes green, and takes over the function of photo- 

 synthesis. This is seen in the tropical Euphorbias, and Cactaceae : 



B.B. O 



