CHAPTER XXIII 
XEROPHYTES 
201. Adaptations.—The adaptations of plants to meet 
drought are numerous and striking. The meager supply 
of water available for the plant must not escape from it 
too freely, and hence most of the special adaptations are to 
check the loss of water. In addition to this, there is often 
developed water-storage tissue, which acts as a reservoir, 
receiving water at a time of supply and doling it out accord- 
ing to the needs of the plant. 
Drought conditions vary in different regions, and may 
be grouped under three heads: (1) possible drought, which 
occurs at irregular intervals, or which in some seasons may 
not occur at all; (2) pertodic drought, which occurs at regular 
intervals; and (3) perennial drought, which is a constant 
condition, as in arid or desert regions. For the first con- 
dition plants are poorly prepared, but by various temporary 
expedients may resist until the drought ceases. For the 
second condition plants are well prepared, enduring the 
regularly recurring drought as definitely as a regularly re- 
curring winter. In the third condition plants not only must 
endure drought, but also must be able to work in such con- 
ditions. 
Some of the conspicuous methods of protection against 
drought have been described (§ 17). These should be kept 
in mind when the following illustrations of xerophytic asso- 
ciations are considered. 
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