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,! 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. 
