14 MASSACHUSETTS HORTICULTURAL SOCIETY. 



It is a well-known fact that the yeast used in making bread and 

 the "mother" used in making vinegar are nothing but an aggrega- 

 tion of "yeast plants," as it were. When the yeast is added to 

 bread under warm, favorable conditions it begins to grow and in its 

 growth liberates carbonic acid gas which causes the bread to rise 

 and become light and porous. In the case of vinegar, a ferment 

 or "yeast plant" attacks the sugar of the cider and converts it into 

 alcohol; then the "mother" of vinegar (another kind of bacteria) 

 attacks the alcohol and converts it into an acid which we call 

 vinegar. 



Similar forms of life are at work, under warm, favorable condi- 

 tions, in the soil preparing plant food for assimilation. Not only is 

 warmth and the right proportion of moisture necessary for their 

 growth but the soil must be neutral or slightly alkaline for their 

 highest development. In order to produce this condition, an appli- 

 cation of quicklime or unleached wood ashes is frequently necessary 

 to correct any acidity of the soil resulting from organic acids which 

 are produced under certain soil conditions. 



All organic matter or substances which have been at some time 

 organized into plants by the life force, such as leaves, roots, stems, 

 etc., must decay before they can nourish; that is, before they can be 

 absorbed and reorganized again into growing crops. Stable manure 

 contains some soluble salts which are immediately ready to feed 

 the crop, but the bulk of the manure must rot down through the 

 influence of bacterial action before it becomes food; and the process 

 of decay or rot is largely the result of the growth of lower forms of 

 life or "yeast plants" in the manure or in the soil, which, as we 

 have seen, are dependent upon certain favorable conditions. 



There are several known forms of nitrogen organisms in the soil ; 

 two that are well defined, the de-nitrifying and the nitrifying, the 

 destructive and the constructive. Touching the various organisms, 

 Prof. Stone of the Massachusetts Agricultural College, writes : 



"The de-nitrifying organisms are those which convert nitrates 

 into nitrites and ammonia. The nitrifying organisms are those 

 which convert ammonia into nitrites and nitrates. The latter are 

 exceedingly beneficial, while the former are not considered so, as 

 plant food must be in the form of nitrates. We never find nitrites 

 in plants. There is another type of organism known as nitrogen 



