258 FIRST YEAR SCIENCE 



which are able to make the best possible use of the avail- 

 able moisture. In dry regions the plants are few and so 

 constructed that little moisture can be evaporated from 

 them. In dry desert regions, except where water finds its 

 way to the surface in considerable quantity, forming oases, 

 there can be but little forage for animals, and what there 

 is, is scattered. The desert animal must therefore be a 

 wanderer, able to subsist upon meager fare. 



This is true of the human inhabitants of the desert as 

 well. They must rove about in small bands living in 



A WATER HOLE IN THE DESERT. 



tents, picking up a precarious living for themselves and 

 their animals, and they must be hardy and capable of 

 withstanding privation. They must move rapidly and 

 carefully over the long distances separating the patches 

 where food can be found. They must therefore be fine 

 horsemen, like the Arabs of Arabia and the Sahara, or 

 strong and swift runners, like the Indians of the south- 

 western United States. 



The life of man on the oases, although much less miser- 

 able than that on the desert, is subject to great disadvan- 



