8 THE CHEMISTRY OF THE FARM. 



action becomes manifest. The oxidation of matters already 

 formed is an important means for the production of new 

 bodies. 



3. Transpiration. Another important function of 

 leaves consists in the transpiration of water. This 

 transpiration takes place through the cuticle of young 

 leaves, but in older leaves chiefly occurs through small 

 openings, known as stomata, which are most abundant on 

 the under side of the leaves. Transpiration takes place 

 chiefly in light ; it will occur abundantly, even in an 

 atmosphere saturated with water, if the plant be only 

 exposed to sunshine. The amount of water evaporated 

 from the surface of a growing plant is very large. Land 

 that has lately borne a crop is always much drier than 

 a bare fallow. 



The results of transpiration to the plant are most im- 

 portant, the evaporation of water from the leaves being a 

 principal cause of the rise of the sap, and the consequent 

 drawing up of water from the soil containing plant food 

 in solution. 



Function of the Boots. The roots of a plant are the 

 organs by which it absorbs water from the soil, and with 

 this water a variety of food elements are introduced. 



1. Assimilation of Ash Constituents. The roots take 

 up the soluble salts, and all the diffusible sub- 

 stances (those capable of passing through a membrane) 

 which are present in the water which they draw from 

 the soil. The plant may thus receive a number of sub- 

 stances not actually required for its nutrition. 



The feeding power of roots is not, however, confined 

 to the taking up of ready-formed solutions, they are also 



