n] FEATURES OF ENVIRONMENT 37 



The general impression is the same in Africa, America 

 and Australia, often to a surprising extent, so that 

 it is difficult to believe that the respective plants 

 have all been evolved out of different and often 

 not closely related families. 



Rain or the seasons produce a marvellous change 

 in the look of many a semi-desert. Within a few 

 days after a drought of perhaps 13 months the same 

 impressively desolate stretch of North Mexico is 

 transformed into a green prairie with countless 

 blooming bulbs, and there is plenty of animal life. 

 In Turkestan spring comes with a rush. The snow 

 melts rapidly under the warm south wind, a carpet 

 of tulips delights the eye for a few glorious weeks, 

 and in the month of May all this vegetation becomes 

 scorched and shrivelled and vanishes under the hot 

 blasts, the dust and sands of the desert ; and during 

 the long, severe winter it is swept by icy storms and 

 covered with snow. 



Life in the desert is fearfully severe. There is 

 very little competition, a desert fauna is always 

 scanty, and there is plenty of room. But the struggle 

 to make a living and the fight against the elements 

 are so severe, that comparatively few creatures have 

 succeeded in adapting themselves to such a life. 



Let us now consider some of their peculiarities. 

 The northern half of the Old World is divided by 

 a belt of enormous extent, from the Canaries to 



