336 VEGETABLE PHYSIOLOGY 
that to which the term Xerophytes has been applied. 
These inhabit different situations, all of which are charac- 
terised by presenting to the plant a very small supply of 
terrestrial water. Many grow in sandy deserts, exposed to 
great heat, and frequently undergoing long periods of 
drought. Others grow upon a rocky substratum, and their 
roots are confined to the crannies and crevices which are 
present in the rock. Others are found in more temperate 
countries, occupying light sandy soils which cannot retain 
any considerable quantity of water. Such xerophytic plants 
as are woody in habit frequently show considerable ten- 
Vic. 143.—Lear or Sazxifraga imcrustata, SHOWING ABSORBING ORGAN. x 20, 
dency to diminish their leaf-surface, probably to reduce 
evaporation and conserve their stock of water. They often 
have many of their branches transformed into thorns or 
spines, and very frequently their leaves show similar reduc- 
tion. Others which contain little wood are succulent, and 
their surfaces are covered by a very thick and tough 
epidermis, which is strongly cuticularised. Many of those 
which grow upon rocks have leaves which show special 
structures for absorbing water from rain or dew. Several 
species of Saxifrage possess a number of glandular struc- 
tures upon the teeth of their thick narrow leaves. Each 
consists of a small mass of cells with delicate walls, which 
