138 PLANT LIFE 



part of the more intolerant trees such as the 

 lime. The evergreens, on the other hand, are 

 usually very long suffering, but, as we have 

 seen, a severe diminution of water supply is, 

 or may be, followed by the hurrying up of 

 those internal processes which culminate in 

 the differentiation of the separation layer at 

 the base of the leaves. 



Thus a plant which is fitted for average 

 conditions of water supply (and is often there- 

 fore called a Mesophyte) may assume certain 

 of the distinctive characters of plants fitted 

 for dry conditions, when its supplies of water 

 are from any cause suddenly interfered with. 

 Plants which are specially adapted to dry 

 conditions are called Xerophytes, and they 

 are directly contrasted with the Hygrophytes, 

 i. e. with those restricted to very wet 

 surroundings. 



In the examples we have just considered, 

 the adaptedness to dry or xerophytic condi- 

 tions is attained by reduction of the transpiring 

 surface. This is a very common feature of 

 xerophytes, 1 and it forcibly illustrates the 

 limitation of one important function (that of 



1 Not all plants with reduced leaf surface are xero- 

 phytes. The large Water Rush (Scirpus lacustris) used in 

 the manufacture of rush-bottomed, chairs is an instance. 

 The reduction of the leaves, and the transference of the 

 photosynthetic function to the stems of these plants is 

 certainly to be correlated with mechanical requirements. 

 A plant built on the plan of the water rush would 

 be an impossibility if any weight of green foliage had to 

 be sustained. 



