PROGRESS OF AGRICULTURAL SCIENCE. 501 



will not grow for many years in succession on the same land, and 

 other crops must be introduced to put the soil in suitable con- 

 dition for growing it again. The cereals with their different 

 requirements, through their reactions upon the soil, which are 

 undoubtedly aided by their associated microbes, and even the 

 roots and companion microbes of other leguminous species, may 

 have a direct influence in determining conditions of the soil that 

 favor the nutritive processes of the clover roots and their specific 

 symbiont microbes. 



The interdependent biological relations of different farm-crops, 

 and of the soil-microbes that find favorable nutritive conditions 

 in the vicinity of their roots, appear to be quite as important 

 factors in farm economy as the chemical composition of soils and 

 crops, and the conditions of the soil that influence these relations 

 are of great practical interest. 



In the light of our present knowledge, it must be obvious that 

 the applications of science to agriculture, so far as crop-growing 

 is concerned, will be best promoted by investigations relating to 

 the life history of these microbes, and their immediate and remote 

 relations to the roots of plants of different species, and to pro- 

 cesses of metabolism in the soil under different conditions. 



The suggestion made by Dr. M. T. Masters, in his Plant Life 

 on the Farm, that in the future the farmer may be able to apply 

 the ferment-producing germs to his soil, to promote the growth 

 of his crops, with greater advantage than he now derives from 

 the application of chemical manures, seems to be fully warranted 

 by the results of recent experiments ; and it may be that the 

 breeding of beneficial microbes may come to be of as great prac- 

 tical interest to the farmer as the breeding of yeast now is in the 

 manufacture of beer. 



We must not, however, be misled by the plausible inferences 

 that may be made from the evidence presented in regard to this 

 recently discovered source of nitrogen supply to leguminous 

 plants under special conditions. It is not safe to assume that 

 the nitrogen removed from the soil by crops and by drainage, or 

 otherwise, is fully restored by corresponding amounts derived 

 from free nitrogen through the agency of microbes, or that this 

 is the sole or even the main source of the nitrogen of leguminous 

 crops on average soils. 



The Rothamsted experiments show that the previous accumu- 

 lations of combined nitrogen in the soil must be the source of a 

 large proportion of the nitrogen of leguminous crops, and that 

 the frequent repetition of such crops does not prevent an appre- 

 ciable diminution of the nitrogen of the surface soil. 



The evidence we now have seems to indicate that, under ordi- 

 nary conditions of farm practice, the microbes concerned in work- 



