54 THE NEW BUSINESS OF FARMING 



the roots of plants give off substances that are 

 poisonous to plants of the same species. By a 

 change of crops these toxines are neutralized 

 and the soil is made wholesome once more for 

 the original crop. 



Plant food, to be available for the growing 

 crop, must be supplied in a soluble form in con- 

 tact with the roots of the plant. Plant food is 

 made soluble by the decomposition of organic 

 matter and disintegration of mineral matter. 

 Humus, or vegetable matter, in the soil hastens 

 this process. Moisture is usually present when 

 humus or partially decayed manure is in the 

 soil, and such material permits a free circula- 

 tion of air and prevents baking or packing of 

 the ground. Decomposition of vegetable matter 

 takes place as the result of bacterial action. 

 These bacteria can only work in the presence 

 of air and moisture, hence the necessity of 

 humus. This decomposition forms acids which, 

 in turn, disintegrate mineral matter. 



The entirely supposititious case of the Stand- 

 ard Oil Company's throwing away aniline dyes 

 and purchasing coloring matter for their kero- 



