SOILS 87 



is not only an important plant food, but it carries to 

 the stalk and leaves nearly all the other foods they 

 need. After traveling through the rootlets up the 

 stem to the leaves, the water that is not needed 

 passes off from the leaves into the air. Therefore 

 we see that plants take in much more water than 

 they can use, for the sake of the food that the water 

 brings with it. We are told that timothy hay needs 

 three hundred tons of water to obtain the other 

 foods necessary to make one ton of hay; oats require 

 five hundred tons of water for a ton of plant. 



Other Food. A bundle of wheat as it comes from 

 the self-binder weighs about ten pounds, and nearly 

 nine and one-half pounds of this is composed of 

 water and the carbonic acid of the air. A large 

 part of the farmer *s labor is done to supply the 

 elements that make up the other half pound of this 

 bundle of wheat. It contains ten simple foods and 

 no two in equal amounts. The wheat cannot spare 

 any one of these ten plant foods. So when the soil 

 loses one element of wheat food, it is no longer good 

 wheat land. 



Humus. Different parts of the same fields may 

 have different colors. The red color of some clays is 

 due to the iron in them, but the brown or black color 

 of soils is usually due to l:lie humus that they con- 

 tain. Humus is the decay of plants. The leaf mould 

 which we find under the dead leaves in the woods 

 is a good sample of humus. This is a very impor- 

 tant element in soil. Humus not only makes the 



