144 PLANTS OF DRY CLIMATES, ETC. [CH. 



not established by scientific evidence with regard to any 

 plant, that its leaves must be modified in any particular 

 direction to meet such conditions as have been referred 

 to ; nor is it proved that any of the peculiarities of struc- 

 ture mentioned are adaptations solely against drought. 

 For, with regard to the first point, we find leaves meeting 

 the exigencies of a dry climate in very many different 

 ways ; and, with regard to the second, a structural peculi- 

 arity may serve one plant as a protection against drought, 

 and another plant in an apparently very different 

 environment may exhibit similar structural variations 

 adapted to meet quite another chain of vicissitudes. All 

 that can be said at present, while this subject is in its 

 infancy, is that plants which flourish in excessively arid 

 situations, invariably exhibit peculiarities which suggest 

 adaptations to the peculiar circumstances. This matter 

 is so important, and misapprehensions have given rise to 

 such strange mis-statements, that I may illustrate it by 

 a few further examples. 



In a region where the spring is marked by two or 

 three months of wet weather, while all the rest of the 

 year is a season of drought, numerous plants with very 

 different habits may exist. Some are short-lived annuals : 

 their seeds germinate and the shoots bear typical flat 

 thin leaves, the flowers appear early and the fruit and 

 seed ripen rapidly, so that the whole life-cycle is com- 

 pleted by the time the dry season sets in. Others are 

 bulbous, putting forth their thin leaves quickly in the 

 spring, and maturing as before before the dry season sets 

 in : the bulbs below ground being renewed before the 

 leaves wither away, and remaining buried and dormant 

 during the drought. In such cases the plants or their 

 leaves may escape the necessity of special adaptations to 

 avoid over- transpiration. Many trees and shrubs also 



