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 tQ 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. 



