168 ORGANIC FOOD. 



form very little idea of the wonderful mechanism, 

 or the rapidity of its motion, which exists in the 

 interior of a fruit tree. These cells are very minute, 

 — many of them not more than one-thousandth of an 

 inch in diameter, — and yet grape vines in a warm 

 house often grow from one to two inches on the 

 end of each shoot per diem. 



It must be manifest to all that plants, as well as 

 animals, require food. It remains for us to examine 

 its nature and adaptation. When a plant is burned, 

 a part escapes into the atmosphere, and a part re- 

 mains in the ash. The first we shall call organic, 

 and the latter inorganic. 



I. ORGANIC SUBSTANCES. 



1. Oxygen. Mr. Johnston thus states the sources 

 of this gas : " The water which plants imbibe so 

 largely consists of this gas in great part, being eight- 

 ninths of its whole weight. In this form it is easily 

 decomposed, and yields an inexhaustible supply. 



" The atmosphere contains twenty-one per cent., 

 and the leaves of plants, in certain circumstances, 

 are known to absorb it. 



" Carbonic acid contains seventy-two per cent, of 

 oxygen by weight, and this gas is known to be 

 absorbed in large quantities from the atmosphere 

 by the leaves of plants ; while in solution with Avater, 

 it is absorbed by the roots. 



