zo ELEMENTARY COMPOSITION. [chap. 



4. Now, not only is water absorbed by the root, but also 

 various substances which are dissolved in the water. Hence 

 we find, if we burn a plant carefully, that an ash remains, 

 consisting of such of these substances as are not dissipated 

 by heat, which were absorbed in this way, and which had 

 been made use of by the plant, or stored away in its tissues. 

 Of the simple elements known to chemists, about twenty 

 occur in the ash of the plants ; many of these, however, in 

 veiy minute quantities, and never all in the same plant. 

 Sulphur, phosphorus, potash or soda, lime and silex, are 

 those most generally found. 



5. But if we analyse an entire plant, and not the ash 

 only, we shall find constantly present, besides the above, 

 the elements carbon, oxygen, hydrogen, and nitrogen. And 

 these elements are present, there is reason to believe, in 

 every organized being, whether plant or animal, in combi- 

 nations peculiar to organized beings. Hence they may 

 be called the organic elements., in contradistinction to the 

 (mineral) elements found in combinations which are not 

 peculiar to organized beings, and several of which remain 

 in the ash of plants when burnt. The latter may be called 

 the inorganic elements. 



6. These four organic elements do not exist separately in 

 the plant, but, as we have said, in combination. Thus the 

 carbon is united with oxygen and hydrogen (the two last 

 the elements of water), forming the basis of a series of com- 

 pounds, called ternary compounds because they are com- 

 posed of three elements. The nitrogen occurs combined 

 with the same three elements, with the addition of sulphur, 

 forming a more complex substance, called protoplas7n^ the 

 medium through which all phenomena of vitality are 

 manifested. And these two series of organic compounds 

 stand in remarkable contrast to each other in the plant. 



