30 BRITISH PLANTS 
approach of winter, and are renewed in the spring, the 
plants to which they belong cannot be regarded as true 
hygrophytes (see Tropophytes, p. 57). 
2. Xerophytes. 
Most plants have to face a deficiency of water some- 
times, and if there were no peculiarity of habit or 
structure to prevent them from suffering during these 
periods, their existence would be threatened, and the 
continuance of the race endangered. Every peculiarity 
of habit and every peculiarity of structure or mode of 
growth which enables a plant to get through a period 
when water is lacking either in quantity or quality is 
known as a xerophytic character, and these characters 
may be few or many, slight or pronounced, permanent 
or temporary, according to the conditions which obtain 
in the normal surroundings of the plant. 
Just as the true hygrophyte exhibits adaptations of 
a permanent character towards moist conditions, so a 
true xerophyte shows adaptations of a permanent 
character towards dry. The unfavourable conditions 
may only come once a year, and if the plant meets this 
by some permanent modification in its structure it is 
a true xerophyte. Thus the holly is common in moist 
woods in the West of England. Its leaf is evergreen, 
thick, and shiny—characters associated with deficiency 
of water (p. 39). The deficiency, however, only occurs 
in winter, when, through the coldness of the soil, the roots 
become inactive and lose, more or less completely, their 
‘power of absorption. The holly therefore exhibits 
during the summer characters which are only really useful 
in winter. In other cases, unfavourable conditions occur 
all the year round ; during summer they may be of one 
kind, during winter of another. When this is so, we 
should naturally expect the plants to be equipped with 
permanent xerophytic characters. All true xerophytes are 
evergreen—e.g., yew, heath, pine, ling, box, laurel, many 
succulents, etc. Plants which assume xerophytic char- 
acters only at the approach of winter are tropophytes 
(see p. 57). 
