210 



ELEMENTARY STUDIES IN BOTANY 



leaves have wilted because they have been losing water at a, 

 more rapid rate than it has been supplied to them, and the 

 effect of the sprinkling is to check this loss by developing a 

 moist atmosphere about the leaves, so that it shall not exceed 



the supply that is coming from 

 the roots. In other words, 

 sprinkling provides a dam 

 against water loss, and allows 

 water to accumulate again in 

 the leaves ; so that the water 

 that " revives " wilted leaves 

 is not that which is sprinkled, 

 but that which is coming all 

 the time from the roots and is 

 now allowed to accumulate 

 a little. 



Some of the structures that 

 prevent the rain from soak- 

 ing in are a smooth epidermis, 

 a cuticle, a waxy deposit, felt- 

 like coverings of hairs, over- 

 lapping scales (like shingles 

 on a roof), etc. In the rainy 

 tropics, where this danger is 

 extreme, it is very common 

 for the sunken veins and ribs 

 of the leaves to form a sort 



FIG 176. A leaf of a rainy tropical o f drainage system for carry- 



forest, with a drainage system of 

 sunken veins and i 

 After SCHIMPER. 



spout-like point. 



ing off water, the main 

 channel lying along the mid- 

 rib, which terminates in a long spout-like point (Fig. 1.76). 



125. Protective positions. Leaves are protected against 

 drying air and intense light not only by their structures, but 

 often also by their positions, and such plants are unusually 

 well-equipped to endure exposure. 



