624 POPULAR SCIENCE MONTHLY. 



this operation is the clearing the field of weeds, but, aside from this, the 

 soil is much more productive and, it may be said, more fertile. What 

 is done to the soil in the process of cultivation is to break up the lumps 

 and allow the air to permeate freely, to retain the moisture by making 

 the surface portions fine and porous, thus acting as a ' Campbell 

 blanket,' to mix so thoroughly that the physical affinity of the soil sub- 

 stances becomes changed, the soil being renewed to a very large extent. 

 In this way a farmer can control the fertility without adding any 

 fertilizer. Similar to this is the case already mentioned where the 

 farmer plows under a field of rye. He increases the fertility without 

 adding any fertilizer. 



Land should never be allowed to bake or become hard on the surface. 

 If so, air is kept from the roots of the plants. Baking of the soil can 

 be largely controlled by the farmer with certain crops. It occurs, more 

 or less, after rain, depending upon the character of the soil. This crust 

 should be broken up, and kept broken up, by cultivation. In hoeing 

 weeds a man is fertilizing the soil. "Weeds, therefore, may be of con- 

 siderable indirect benefit. 



The fable of the farmer dying when on the point of revealing great 

 hidden treasure to his sons illustrates the point. When about to die 

 he told his sons that immense treasure lay buried in the ground on the 

 farm, but death came just before he was able to tell the exact spot. 

 His sons then dug through every inch of soil, over and over again, with 

 the greatest diligence, but did not find any such treasure as they ex- 

 pected to find. The result, however, of such thorough digging was 

 great abundance in the crops. They really did unearth the treasure, 

 but in a far different way from that which they expected. 



The bacterial content plays also a very important role in the process. 

 Comparatively little is known in regard to the interrelationship exist- 

 ing among these organisms, and of their relations with plants. The 

 processes of nitrifying and denitrifying are in themselves important, 

 but these are probably only an extremely small part of the bacteriolog- 

 ical question. And chemical analysis of soils does not throw much 

 light upon it. It is a more complicated problem than a mere chemical 

 one. 



Eoot-tubercles and their production, although a bacterial proposi- 

 tion, require, because of their importance, special mention. The organ- 

 ism which produces the tubercle is capable of extracting nitrogen from 

 the air and rendering it available for the plant upon which the nodule 

 is produced. And these nodules are capable of being produced on many 

 plants of the ' bean ' family, such as clover, alfalfa, peas, vetches and 

 the like. The cultivation of such crops, therefore, is productive of 

 additional fertility in nitrogen. The soil, of course, should contain the 

 bacteria peculiar to the plant upon which they work. The soil may 

 contain them already; if not, it should be inoculated. Each farmer, 



