Deserts 



93 



attract the clouds or not, and this still waits for a satis- 

 factory answer; but it is certainly the popular opinion that 

 they do, and it is a very common thing to hear it said that 

 the clouds have gone over to a neighboring park or wood, 

 when the farmer would have been better pleased that they 

 should water his fields. 



As we began by saying, the subject is a difficult one; 

 but though we may not be able to explain precisely the 

 how, there is no doubt at all as to the fact that the 

 presence or absence of all vegetation, not of trees only, 

 does very greatly affect climate, and the climate in its turn 

 affects vegetation. 



For instance, Tacitus, the Latin historian, writing 

 some eighteen hundred years ago, mentions that not even 

 a cherry would ripen on the banks of the Rhine; and he 

 certainly would not have believed that in centuries to 

 come the same region would have become warm enough 

 to be famous for its vineyards. But in his day forests 

 abounded all about the river, and it is the removal, or 

 great diminution, of these which has raised the tempera- 

 ture. A similar, but in this case disastrous, result has 

 been produced on the southern slope of the Pyrenees, 

 where what once were wide fertile tracts, covered with 

 vegetation, have been turned into wastes by the destruc- 

 tion of the forests too recklessly carried out. 



Wooded countries certainly seem on the whole to 

 receive most rain; and the clearing away of any kind of 

 vegetation, be it herbage, brushwood, or forest-trees, may 

 be, and often has been, attended by evil consequences. 

 For vegetation protects the soil from evaporation, enab- 

 ling it at least to keep what water it receives; and as this 

 accumulates, springs or reservoirs are formed, from 



