LEGUMINOUS ROOT TUBERCLES . 223 



leaf tissues. A single leaf may have several dozen of these symbiotic 

 bacterial nodules. Faber has shown that the leaves of these rubiacfeous 

 plants through the presence of the nodules containing bacteria are able 

 to gather nitrogen like the legumes and store it in the small nodules. 

 As the value of the leaves of these plants in agricultural operations in the 

 tropics has been recognized in India, it has been suggested that these 

 nitrogen-storing members of the Rubiacea might be grown as subsidiary 

 crops beneath rubber, cocoa and coffee trees and their leaves allowed to 

 accumulate on the ground to serve as a mulch and as a nitrogenous 

 fertilizer. It might be possible to prune the trees and use the clippings 

 as fertilizer. 



Use as Green Manure. When the leguminous crop is mature, or 

 before it is mature, it 'may be plowed under as green manure. Here 

 in the soil by the process of putrefaction already described, the organic 

 nitrogen of the plant is converted into a form of nitrogen which through the 

 nitrifying bacteria is again converted into a form (nitrate) available to 

 another crop of green plants. Thus the nitrogen cycle is completed. 

 Or, if the leguminous crop is not used as a green manure, but is consumed, 

 it should be used on the farm and not sold off the farm, because transformed 

 by passing through the bodies of the farm animals, it becomes flesh on the 

 one hand and barnyard manure on the other, which can be restored to 

 the soil to help keep up its fertility. 



Rotations. One of the approved methods of agricultural practice is 

 to grow leguminous crops for home consumption, and the non-leguminous, 

 nitrogen-consuming crops for sale. One practical farmer grows mixed 

 crops of leguminous plants, liberally fertilized with potash and phosphoric 

 acid. He converts the first year's crop into silage, which he feeds to 

 his cattle, returning the manure to his soil. He converts the second 

 year's produce into hay. The land thus produces highly nitrogenous 

 crops without purchasing outside supplies of expensive nitrogenous fer- 

 tilizers, and is left in a high state of fertility for potatos or cereal crops 

 which respond to rich supplies of nitrogen in the soil. 



Encouragement of Leguminous Crops. Having ascertained these 

 facts, the question naturally arises, How can the growth of leguminous 

 plants be encouraged? It has been discovered that leguminous crops 

 require considerable supplies of potash and phosphatic fertilizers. Potash 

 has considerable to do with the metabolism concerned in the formation of 

 carbohydrates, and phosphorus compounds have to do with the nitrogen- 



