THE KEY-NOTE OF GOOD FARMING. 27 



roots of the plant, and holds it in its position; absorbs the 

 heat, air, and moisture which are required to be about them ; 

 and contains in very small quantities, certain materials which 

 are necessary to growth, and which can be supplied only by the 

 soil. 



Nitrogen and carbonic acid, which are absorbed by the roots, are 

 necessary constituents of the soil, but as they come originally from 

 the air, I have deemed it best to postpone their consideration. 



THE AIR. 



The air, like the soil, consists of an immense bulk of ma- 

 terials which, so far as the growth of plants is concerned, have 

 mainly a mechanical action. This immense mass contains car- 

 bonic acid in the proportion of about one part to twenty-five 

 hundred, and ammonia in very much smaller proportion ; it also 

 contains very varying, amounts of watery vapor. These three 

 substances, — for, although only thin air to our senses, they are as 

 substantial as the soil itself, and can be weighed, and measured, 

 taken apart and put together again with as much accuracy as 

 though they were wood or stone, — are the great sources of the 

 material of which all plants are composed.* All of the plant, 

 whether the smallest grass or the largest tree, is made up of the 

 constituents of water ^ carbonic acid^ and ammonia ; save only the 

 small part that remains as ashes after burning. 



One thousand pounds of red clover hay, out of which the 

 water had been dried, contained — 



Ash 77 lbs. (from the soil.) 



Carbon 474 " ( '• carbonic acid.) 



"y'^''°g'^" 50 " |( . ^3,er.) 



Oxygen 378 « J ' 



Nitrogen 21 " ( " ammonia.) 



1,000 lbs. 



* As in the case of some of the minerals in the soil, I make no account in this con- 

 nection of nitric acid, nor of the many gaseous results of vegetable and animal decompo- 

 sition, as I desire to state the leading principles of growth in the simplest form possible. 



So far as these gases are definitely known to have an influence on vegetation, 



