NEW PRACTICE. 275 



it is not strange that the scientific rotation of crops for the 

 conservation of soil fertility is absolutely new practice in nine- 

 tenths of the cultivated counties of the country. The new 

 rotation always involves one of the legumes peas, beans, 

 crimson clover, alfalfa, or some plant of this species. These 

 have the power, through the bacteria which dwell in sym- 



CH AFTER VIII., FIG. 76. MILKERS IN UNIFORM. 



biotic relation with their roots, of transforming the nitrogen 

 of the air into available plant food and, after the crop is gath- 

 ered, of supplying to the soil for the benefit of the succeeding 

 crop, of whatever nature, large quantities of this vital ele- 

 ment. Since the supply of nitrogen is the main factor in the 

 expense account where a fertilizer is used at all, it is obvious 

 that if a crop can be grown which will bring into the soil this 



