14 QUARTERLYJOURNAL. 



Animals whose organized tissues are composed of thess princi- 

 ples are incapable of forming them from their elements, and hence 

 must receive them ready formed in the flesh of other animals or in 

 vegetables. All the albumen, fibrin and casein now existing in 

 animals must have previously existed in vegetables, which are the 

 grand agents for forming organic compounds for the use of animals. 



Plants contain then, two classes of substances: 



1. Inorganic constituents consisting of salts of soda and potash, 

 of silex, alumina, &c., which are deposited in, but do not form a 

 part of the organized tissues. These constitute mainly the ashes 

 of plants when burned. 



2. Organic matter composed of three elements : carbon, oxygen, 

 and hydrogen — or of four elements, nitrogen being added to 

 these three. These elements are united together in the living 

 plant under conditions which cannot be reproduced by any artifi- 

 cial means, and form what are called proximate principles. 



Now that we have an idea of the composition of plants, we 

 proceed to the consideration of their food. 



As we have established two classes of substances entering into 

 the composition of plants, viz., the organic and the inorganic mat- 

 ters, so we may establish a corresponding division of their food. 

 I will consider each of these divisions separately. 



1. Of the materials out of which the organic matters or proxi- 

 mate principles of plants are formed. 



There are four articles of food out of which plants form all their 

 proximate principles or organic constituents. They are 



1. Water, composed of hydrogen and oxygen. 



2. Carb. acid, " " carbon and oxygen. 



3. Ammonia, " " nitrogen and hydrogen. 



4. Nitric acid, " " nitrogen and oxygen. 



It will be seen that the two first of these substances (water and 

 carbonic acid) contain the elements of the non-nitrogcnized princi- 

 ples of plants. For if from the carbonic acid we subtract the 

 oxygen, we have carbon remaining, which by its union with the 

 elements of water jn different proportions, forms starch, gum, 

 sugar and the other principles of that class. 



For the formation of the nitrogenized principles we must have, in 

 addition to these elements, nitrogen, which is derived from ammonia 

 or from nitric acid. 



