THE YEAST OF THE SOIL. 15 



fixation organisms, and are represented by the organisms in legume 

 nodules; also by many free organisms which exist in the soil. We 

 do not know much about these organisms, but we do know that there 

 are quite a number of them. Some of them appear to work better 

 when living with other organisms than when isolated by them- 

 selves. There is evidence to show that a large number of organisms 

 have the power of fixing nitrogen in the soil ; for example, besides 

 the species of bacteria, there is evidence to show that many of the 

 algae which live in the soil and certain molds will do the same thing. 

 In our work here, we find the largest percentage of nitrogen in those 

 solutions which are contaminated with the blue bread mold (Pen- 

 cillum), showing that it is a nitrogen fixer. I think it will be shown 

 later on that c{uite a little nitrogen is fixed in the soil by this tv^je of 

 organism, exclusive of those on the nodules of the legumes. The 

 de-nitrif}ang organisms are often found in manure piles and are 

 responsible for the liberation of ammonia and, as such, we would 

 not consider them favorable." 



In the spring of the year, when the weather conditions are usually 

 unfavorable for the propagation and rapid multiplication of these 

 soil "yeast plants," commercial manures are found of great assist- 

 ance in forcing an early growth by suppliying forms of plant food 

 which have been rendered soluble by chemical treatment or are, 

 so to speak, predigested and ready for the crop to feed upon 

 immediately. Since most of our cultivated crops make their chief 

 growth in from sixty to ninety days, it will be clear that we must 

 have plant food in the soil that will feed the plant from beginning 

 to end, especially in the beginning of the season when the bacteria 

 of the soil, owing to weather conditions, have not gotten under way. 



The Modern Explanation of Composting, Drainage, and 



Cultivation. 



The discovery of soil bacteria, which also exist in stable manure, 

 explains the advantage of composting and cultivation for forcing 

 early growth. In the majority of cases it is no doubt cheaper if not 

 better to apply stable manure in its crude state directly to the soil ; 

 to cultivate it into the soil and allow the bacteria to attack it there; 



