436 NATURE AND PROPERTIES OF SOILS 



bacteria diffuse themselves more or less through the tissues of 

 the root. What part the bacteroids play in the transfer of 

 nitrogen is not known. It has been suggested that in this 

 form the nitrogen is absorbed by the tissues of the plant. It 

 seems quite likely that the nitrogen compounds produced 

 within the bacterial cells are diffused through the cell-wall and 

 absorbed by the plant. 



240. The practical importance of B. radicicola. — The 

 nitrogen fixed by the nodule organisms may go in three di- 

 rections in the soil. It may be absorbed by the host plant, 

 the latter benefiting greatly by the association. This rela- 

 tionship has already been discussed. Secondly, the nitrogen 

 may pass in some way into the soil itself and benefit a crop 

 associated with the legume. Thirdly, the nodules may decay, 

 when the legume dies or is turned under, the nitrogen be- 

 coming available to the succeeding crop. 



The relationship between associated legumes and non- 

 legumes has been particularly studied by Lyon and Bizzell 1 

 and by Lipman. 2 It has been quite definitely proven that the 

 non-legume may be greatly benefited by the association under 

 some conditions. This accounts for the practice of growing 

 timothy with clover, which has been common for centuries. 

 Just how the transfer of nitrogen is facilitated yet remains 

 to be shown. 



The beneficial influences of such legumes as clover, vetch, 

 and alfalfa on the succeeding crops has long been taken ad- 

 vantage of in practical agriculture. Until recently the stimu- 

 lation has been ascribed to an actual increase of nitrogen in 

 the soil, due to the growth of the legume and the activity of 

 its nodule organisms. This will not always account for the 

 phenomenon, since it has been shown by a number of investi- 



1 Lyon, T. L., and Bizzell, J. A., Availability of Soil Nitrogen in 

 Relation to the Basicity of the Soil and to the Growth of Legumes; 

  Jo 2 ur \ Ind - and En g- c hem., Vol. 2, No. 7, pp. 313-315, 1910. 



2 Ldpman, J. G., The Associative Growth of Legumes and Non-Legumes. 

 N. J. Agr. Exp. Sta., Bui. 253, 1912. 



