Deserts 109 



otherwise, if cut first near the p^round, almost the whole 

 of the water will have rushed away into the vine high 

 overhead before the second cut can be made. 



This plant therefore seems to dispose of a pint of 

 water in less than a minute, and almost all by tran- 

 spiration, since the quantity evaporated and the 

 quantity required for growth, in one minute, must be 

 exceedingly small. At this rate the liana pumps up 

 from the ground 60 pints of water in an hour — 720 

 pints, or go gallons, in a day of twelve hours. 



In early spring, when the sap is beginning to rise, the 

 sugar-maple will sometimes yield as much as seven or 

 eight gallons every day for three weeks, and this, of 

 course, does not represent more than a small portion 

 of the water which the tree has taken up, as it is only 

 tapped, not drained of moisture. But the maple is 

 far outdone by the Black Birch, another of the 

 American trees from which sugar is made ; for one 

 specimen of this yielded, in four or five weeks, the 

 extraordinary quantity of about i,8go gallons. And 

 this, like the sap yielded by the maple, is only a part, 

 and a small part, of the moisture which the tree has 

 drawn from the earth, and would in the natural course 

 of things return to the air, diminished only by the small 

 supply needed for fresh shoots and leaves. 



But the amountof water which a plant takes up doe3 

 not depend solely on the aoil and climate in which it 

 grows, but also on the plant itself. There is a 

 wonderful difference in the power which plants possess 

 of supplying themselves with food and water. Just as 

 one man will live, and even thrive, where another would 

 starve, so it is with vegetables. The lichen makes a 

 living off the bare rock, where nothing else can grow ; 



