Deserts 8c 



tion, 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 

 sixty pints of water in an hour — seven hundred and twenty 

 pints, or ninety 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 

 eighteen hundred and ninety 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 amount of water which a plant takes up does 

 not depend solely on the soil 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; and the ice-plant car- 

 pets some of the most arid rocks of Greece, even after 

 months of drought, and looks, too, just as deliciously cool 

 as ever, its fleshy leaves being still covered with their 

 characteristic "frosting," against which the hottest sun is 



