3 THE COW PEA. 



that legumes, or pod-bearing plants, are capable of growing 

 on artificial soils originally wholly devoid of nitrogen. 

 This led to the discovery that legumes have the faculty 

 of taking up the free nitrogen of the atmosphere, holding 

 it fast and mingling it with the soil, a discovery of the 

 greatest importance, in view of the fact that plants of other 

 families wholly lack this power to make use of the unlim- 

 ited air supply of nitrogen constantly surrounding them. 



Nitrogen is one of the three necessary fertilizer ele- 

 ments, and at the same time the most expensive. It forms 

 but two or three per cent, of the weight of common plants, 

 but it is absolutely necessary to their growth. About four- 

 fifths of the weight of air is nitrogen, and in the air resting 

 upon a farm there is nitrogen enough to produce many 

 crops, yet such plants as corn, wheat, potatoes and cotton 

 cannot utilize it, and so may be starving, though surrounded, 

 literally enveloped, with plenty. It is of no more use to 

 them than the waters of a lake would be to a man floating in 

 it in a water-tight cask. This is not true of the cow pea and 

 legumes, or pod-bearing plants, so markedly possessing the 

 rare faculty of utilizing the nitrogen of the air. They use 

 this atmospheric nitrogen to build up their own plant tissue 

 and convert it imo such forms that other plants can use it. 

 Those who have u^ed nitrate of soda know that it will show 

 in crops quicker thari cotton seed meal or tankage. Yet, 

 after the latter has been in a warm, damp soil for some 

 time, it also becomes available and the plant quickly 

 responds to its use. Though the meal, the blood, and the 



