LOSS OF WATER 
39 
but thoroughly wet the walks and walls so as to maintain 
a favorable humidity of the air. 
Naturally, anything that tends to increase humidity 
will retard transpiration. If the air in the vicinity of 
foliage is quiet, its humidity will increase owing to the 
FIG. 31. Transpiration from four leaves of oleander. At the left, 
both sides coated with cocoa butter; next, under surface, only, coated; 
next, upper surface, only, coated; right, uncoated. All exposed for the 
same length of time. 
water-vapor from the leaves, but when the wind blows, 
fresh portions of less humid air are continually brought 
into contact with the plants, and transpiration becomes 
more rapid. This is why a plant or a bouquet, being 
carried from one place to another, will keep fresh longer if 
wrapped with paper. 
