THE COW PEA. 33 



undertaken to solve this problem, demonstrated the fact 

 that leguminous, or pod-bearing plants, are capable of 

 growing on artificial soils originally wholly devoid of nitro- 

 gen. This led to the discovery that legumes had the fac- 

 ulty of taking up the free nitrogen of the atmosphere hold- 

 ing 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 the most expensive, and at the same time, 

 one of the three necessary fertilizer elements. It forms but 

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

 it is absolutely necessary to their growth, without it their 

 development is impossible. Now the air contains about 

 four-fifihs of its weight in nitrogen, and in the air rest- 

 ing 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 surrounded, liter- 

 ally 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 are 

 able to absorb this atmospheric nitrogen and convert it 

 into such forms that other plants can use it. Those who 

 have used nitrate of soda know that it will show in crops 

 quicker than cotton seed meal or tankage. Yet, after the 

 latter has been in a warm, damp soil for some time, it also 



