PLANT CHEMISTRY 99 



half of every tree to supply food for new ones, for the roots 

 rot in the ground, and the branches rot on the surface, while 

 only the trunk is carried away. But when the farmer carries 

 away from his fields the stalks and the ears of corn, digs up 

 his potatoes and hauls away their tops, and takes both 

 the seed and the straw of his grain, then he is taking away, 

 so most chemists agree, more than the soil is able to replace. 

 If this goes on year after year, the fields are starved, the plants 

 spindle, and the farm is finally abandoned by the discouraged 

 owner. 



If a man wishes, therefore, to keep his farm or his garden 

 in condition to yield well, he must return to the soil as much as 

 he takes away. In this way the garden becomes a factory. 

 Into it he puts cheap chemicals, the "raw materials" of his 

 crops. The garden turns these into expensive chemicals, the 

 crops themselves. These he sells or uses, and thus he makes 

 his profit. 



The chemicals which he applies to the soil may first be 

 other crops, grown at a convenient time, and plowed under 

 in order to rot. Clover, vetch, rape, and rye, are often used 

 in this way. The chemicals may be, occasionally, parts of 

 the crop that used to be carried off. Thus on large wheat 

 farms the farmer may harvest only the seed, leaving the straw 

 to be plowed down. Manure contains chemicals which are 

 valuable for plants. But in most cases the chemicals which 

 the farmer supplies are minerals. They are bought by the 

 ton or by the bag, look often like dirty table-salt, are scat- 

 tered on the surface, and are plowed or harrowed into the 

 ground. 



It is odd to think that we can feed plants in this way, and 

 that ground rock can beautify our gardens. The fact is, 

 however, that we may use not only this but other things, for 

 fertilizers. Material which otherwise would be thrown away 



