218 SYSTEMS OF PERMANENT AGRICULTURE 



normal amount of available nitrogen, the growing of such legumes 

 would enrich the soil in proportion to its poverty. In other words, 

 to the soil that hath not, shall be given; but, from the soil that 

 hath, shall be taken away. 



When properly infected, legume plants have power to make nor- 

 mal growth and full development on soils absolutely devoid of 

 nitrogen, if available mineral plant food, limestone, moisture, 

 aeration, and all other essential factors are provided in abundance 

 or perfection; and the statement sometimes made that the pres- 

 ence of soluble nitrogen is necessary, in order to give clover a start, 

 is not correct, as witness the accompanying illustrations of clover 

 growing in purified quartz sand void of nitrogen, with all plant food 



provided except nitrogen, the culture on the right marked "Bac- 

 teria " having been well inoculated with the clover bacteria; 

 while the middle culture was started in exactly the same manner, 

 except that it was not inoculated. In the culture on the left, all 

 plant food was provided, including nitrogen. 



NITROGEN IN TOPS AND ROOTS OF LEGUMES 



From data already given it will be seen that in the study of 

 immature cowpeas at the Illinois Station, the infected plants 

 contained only 14 per cent of their total nitrogen in the roots with 

 more than half of this in the tubercles themselves, at that stage of 

 growth. As the plants approach maturity, the tubercles decay, and 

 only the shell, or outer coat, remains, the nitrogen being absorbed 

 largely by the host plant, but in some part evidently by companion 



