49 



can exist ; from the first indications of the germi- 

 nation of the seed, till the ripening of the grain, water 

 is always the first stimulator and supporter of life. 

 A great deal of the water which serves to convey to 

 the plant the necessary food from the soil, is, as I have 

 mentioned before, evaporated through the stomata 

 of the leaf; but the quantity exhaled depends 

 entirely on the amount of moisture already present 

 in the atmosphere. This process of absorption and 

 evaporation has been compared by some one to the 

 burning of a wick fed by oil : the greater the evapo- 

 ration of water through the leaves, the larger the 

 flame of the wick the greater the consumption of 

 oil, the more rapid the circulation of the sap. 



Leaves not only exhale, but also inhale, watery 

 vapour, and that with great rapidity whenever the 

 soil becomes dry and the roots cannot find sufficient 

 moisture for the purposes of the pknt. The bene- 

 ficial effect of dew is entirely owing to this peculiar 

 property of the leaves. Thus it can be explained how 

 trees in India preserve their beautiful green foliage 

 throughout the dry season, when not a drop of rain 

 moistens the ground for months. These plants 

 seem to store up during the monsoon sufficient 

 inorganic food within their cells to meet their 

 requirements throughout the remainder of the year ;. 

 and a wise Nature has given to the leaves the power 

 to absorb sufficient moisture from the atmospheric 

 air to maintain the circulation of the sap. 



