FOODOFPLANTS. U 



to call attention to their views and render them intelligible to a 

 class of persons who do not possess the knowledge of chemical 

 principles which these works suppose in their readers. 



Let us first of all see what is the composition of the matters 

 found in plants, and we will be better prepared to understand the 

 nature of the food and the changes it undergoes. 



A superficial examination of the composition of plants shows 

 that they contain gum, starch, sugar and other matters of like na- 

 ture, which are not found in the soil nor in the atmosphere. The 

 plant must, then, by virtue of forces peculiar to itself, form these 

 matters out of the materials it derives from these two sources. 



But we must look more closely into the composition of plants. 



If we burn a plant in the open air, a large portion passes off in 

 the form of vapor of water and of gas, and a quantity of ashes 

 remains. 



This ash of plants which cannot be dissipated by heat, is found 

 on analysis to be composed of salts of soda and potash, alumina, 

 silex and other earthy and saline matters. These matters are es- 

 sential components of the plant, but do not seem to have made 

 part of its organized tissues. They are simply deposited in these 

 tissues, and are called the inorganic constituents of plants. Lie- 

 big has called especial attention to their importance in vegetation. 



Those parts which pass off in a gaseous state during combus- 

 tion are the organized parts and organic products of the plant. 

 If we collect these gases and this vapor, we find that on ultimate 

 analysis they may all be resolved into four elements, carbon, oxy- 

 gen, hydrogen and nitrogen. There are also some traces of sul- 

 phur and phosphorus. 



We can thus arrive at the first grand division of the constituent 

 parts of plants, viz., the inorganic constituents, composed of 

 earthy and saline ingredients which remain after burning, in the 

 form of ashes, and the organic matters composed of the four sim- 

 ple substances I have mentioned, and which pass off in the form 

 of gas and vapor. 



Carbon, oxygen, hydrogen and nitrogen are then the elements 

 out of which all the organic matters of plants are formed ; but 

 these elements are combined in a manner very different from that 

 in which they are combined in dead matter, and this leads me to 



