THE PLANT. 39 



CHAPTER VI. 



8TAKCH, WOODY-FIBRE, GLUTEN, ETC. 



have hitherto examined the raw material of 

 plants. That is, we have looked at each one of the 

 elements separately, and considered its use in vege- 

 table growth. 



We will now consider another division of plants. 

 We know that they consist of various substances, such 

 as wood, gum, starch, oil, etc., and on examination 

 we shall discover that these substances are composed 

 of the various atnwsphwic and earthy ingredients de- 

 scribed in the preceding chapters. They are made 

 up almost entirely of atmospheric matter, but their 

 ashy parts, though very small, are (as we shall pres- 

 ently see) of great importance. 



These compounds may be divided into two classes. 



The first class are composed of carbon, hydrogen, 

 and oxygen. 



The second class contain the same substances and 

 nitrogen. 



The first class (those compounds not containing ni- 

 trogen) comprise the wood, starch, gum, sugar, and 

 fatty matter, which constitute the greater part of all 

 plants, also the acids which are found in sour fruits, 

 etc. Various as are all of these things in their char- 

 acters, they are entirely composed of the same ingre- 

 dients (carbon, hydrogen, and oxygen), and usually 

 combined in about the same proportion. There may 



