CHAPTER V 



THE VARIOUS SUBSTANCES MADE BY PLANTS, AND THE 

 USES THEREOF TO THEM AND TO US 



Metabolism 



N chapter two of this book it was shown that plants 

 manufacture grape sugar in their lighted green leaves; 

 and I said it would later be proven that this sugar rep- 

 resents a basal food substance out of which, with sundry 

 minor additions, plants build all of their other materials. The 

 time has now come for this demonstration, to which, as a sub- 

 ject possessing perhaps more importance than interest, I bespeak 

 the reader's somewhat spartan attention. Since all of the sub- 

 stances constructed by plants have a meaning in their vital 

 economy, I might also have entitled this chapter "on the various 

 uses that plants make of their food," in which case I should 

 have to commence with a review of respiration, for that is the 

 most important of the uses of food. The others here follow in 

 an order determined chiefly by the chemical nature of the sub- 

 stances concerned. 



The number of substances constructed by plants is verily 

 legion, for the vast variety of foods and fabrics, drugs and dyes, 

 and other materials yielded by them to us is only a small pro- 

 portion of those which they actually make. Fortunately, how- 

 ever, for our limited comprehensions, those which are really 

 important are few, and moreover, they fall into somewhat defi- 

 nite classes. Since the subject is new to most persons, I will give 

 these classes in synopsis as a kind of table of contents to this 

 chapter. They are these: 



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