86 THE CULTURE OF FARM CROPS. 



dium. Though the leaves of plants are continually sur- 

 rounded by nitrogen, and the roots may be bathed in 

 water containing it in solution, yet there is no evidence to 

 show that any plant is so constituted as to avail itself of 

 this supply. Indeed there is a, good deal of evidence to 

 prove that the leaves do not absorb nitrogen and that if 

 any uncombined nitrogen at all is contributed by the at- 

 mosphere and used by plants, it is through the roots that 

 it must enter into their circulation. But that even this oc- 

 curs is a matter of opinion only, with no evidence to sup- 

 port it. 



It is an essential part of good farming to break up the 

 land and reduce it by thorough tillage, by means of the 

 most effective implements, to a loose and mellow condition, 

 so that the air can have access to the decaying organic mat- 

 ter in the soil ; as well as to the living roots which permeate 

 the earth in all directions to considerable depths below the 

 surface. When the air is thus admitted to the roots, it is not 

 impossible that some of the nitrogen, as well as some of the 

 oxygen, may be absorbed and made use of by the plant di- 

 rectly ; but in the changes in the organic matter which oc- 

 cur, it is known that nitrogen is disengaged in a form in 

 which it can be appropriated by plants ; and it is probable 

 that some atmospheric nitrogen may also be seized upon 

 and converted into plant food at the same time. To what, 

 extent this may happen however we have as yet no certain re- 

 sults from which any definite knowledge has been reached. 

 If any nitrogen enters the roots of plants in solution in wa- 

 ter, the quantity is very small and uncertain. 



When water is exposed to the air it gradually absorbs- 

 both oxygen and nitrogen ; as has been previously men- 

 tioned. The whole quantity of these mixed gases thus tak- 

 en up amounts to about 4 per cent, of the volume of the 

 water and in rain water about two-thirds of this quantity 

 consists of nitrogen. A hundred cubic inches of rain water 

 will therefore carry into the soil 2f inches of this gas. But 

 this water in passing through the soil dissolves also other 

 substances; carbonic acid and various solid matters and in 



