1 86 Climate 



But though colour makes such an important differ- 

 ence in the power to absorb heat, it has no influence, 

 apparently, upon the power to retain it. Indeed, 

 though sand may absorb heat less quickly than a 

 darker soil does, when once it is warm it remains warm 

 longer than any other. The coarser it is, too, the less 

 quickly it cools ; and as coarse gravel, once thoroughly 

 heated, retains some degree of heat even through the 

 night, it is found useful to put it round grape-vines to 

 keep them warm. 



Great, and especially sudden, changes of temperature 

 are particularly trying to most plants, though such as 

 grow in deserts have become so accustomed to being 

 scorched by day and frozen by night, as at least to 

 manage to keep alive. But though an even tempera- 

 ture is in some ways most desirable, it does not by any 

 means follow that all plants would thrive in the equa- 

 torial region. That region, as has been said, is charac- 

 terized less by its great heat than by its remarkable 

 uniformity of climate. It knows no change of seasons : 

 it is always summer, always spring, and always autumn 

 there, and many trees bear both flowers and fruit at 

 the same time. But this constant activity, though it 

 suits the trees and plants accustom.ed to it, is too 

 much for our European fruit-trees and other plants ; 

 for these are in the habit of taking a winter sleep, and 

 cannot get on without it. Transported to the equa- 

 torial region, they grow, indeed, freely enough, but too 

 freely; for they become evergreen, putting out fresh 

 leaves all the year round, and are so exhausted for 

 want of their customary rest that they are unable to 

 ripen their fruit. This is the case even when they are 

 taken to the cooler hill-country of Ceylon ; and it is 



