348 WATER MAKES A GARDEN OF THE DESERT 



is not level, the water does not " back up " above it, but flows on- 

 ward parallel with it. In some distant region the underground 

 water finds an outlet for itself and forms a spring (Fig. 213). 



The streams flowing from springs join other streams and 

 these eventually join larger streams or rivers. From the sur- 

 face of the water evaporation occurs, and vapor passes into the 



atmosphere, where it is 

 condensed and again 

 falls to the earth. 



Fertile plains and 

 deserts. A traveler on 

 his way from New York 

 to California leaves re- 

 gions of luxurious vege- 

 tation, passes through 

 dry parched plains 

 clothed only here and 



FlG. 213. How springs are formed. A, porous i i 



layer; B, non-porus layer ; C, spring. there wlth a scant Y 



vegetation, and finally 



ends his journey in a land of rich and varied vegetation. In the 

 East and middle West profitable farming lands appear on every 

 hand, in the far West desert wastes extend as far as the eye can 

 reach (Fig. 214), and not until the lands lying on the Pacific 

 Ocean are reached do vineyards, orchards, and farms reappear. 

 There is only one explanation for these striking contrasts, 

 namely, differences of rainfall. Enough rain falls in one year 

 in the East to make a layer of water about 60 inches deep ; so 

 little falls on the dry western sections that it would take about 

 seven years to make a layer of the same depth. 



Plants, like all other living things, require food. Some of this 

 they get from the air through leaves, some they absorb from 

 the soil through roots. But if the soil is so dry that there is 

 not enough moisture to dissolve soil food, the plant dies, even 



