98 



THE BEGINNER'S GARDEN BOOK 



The matter which remains from a plant after this thorough 

 drying is chiefly some compound of carbon. Carbon we 

 know best as charcoal; but when crystallized it is the dia- 

 mond, or the lead of our pencils ; and when combined with 

 other elements it takes various forms, the chief of which in 

 plants is starch. Finally, besides water and carbon, the 

 most important chemicals in plants are phosphorus, potash, 

 and nitrogen. These, at least, are the elements which it is 



most important for us to supply, 

 since they are the elements with- 

 out which plants suffer. 



We studied in the last chapter 

 how to save water for the use of 

 our plants. Carbon we do not 

 need to trouble about, for the very 

 good reason that plants get most 

 of their carbon from the air. The 

 amount of carbon in any given 

 amount of air is so small that I 

 did not mention it just now when telling what air was com- 

 posed of. In ten thousand parts of air there are but one 

 and a third parts of carbon ; yet so vast is the amount of air 

 over the earth, and so rapidly does it change among the leaves 

 of the plants, that it supplies most of the carbon for all the 

 plants that grow on the earth. 



The other three elements we must supply. But first it 

 may be asked why we have to take pains to supply plants with 

 any food. Truly, in wildernesses no food is supplied by man. 

 The forests grow, and maintain themselves for centuries ; 

 year after year the swamps grow rank with grasses. But this 

 is because that which dies lies and rots on the ground, return- 

 ing to it the food which once it took up. Even when man 

 comes into the forest and takes away logs, he leaves more than 



Fig. 55. — The chemical 

 make-up of a potato. 1 repre- 

 sents water; 2, starch; 3, nitro- 

 gen; 4, all other elements. 



