ON THE GROWTH OF LEGUMINOUS CROPS. 41 



present, and the supply of oxygen is sufficient; but the data at 

 command do not justify the conclusion that these conditions would be 

 adequately available in such cases as those of the very large accumula- 

 tions of nitrogen by the Red-clover grown after the Beans, and of the 

 increasing, and very large accumulations, by the Medicago sativa, for a 

 number of years in succession. 



The alternatives are either that the plant may take up nitrogen 

 from the sub-soil in some other way, as ammonia, or as organic 

 nitrogen ; or that the free nitrogen of the atmosphere is in some way 

 brought under contribution. 



CAN ROOTS, BY VIRTUE OF THEIR ACID SAP, ATTACK, AND RENDER 

 AVAILABLE, THE OTHERWISE INSOLUBLE NITROGEN OF THE SUB-SOIL? 



In reference to the first of the above alternatives, the question 

 suggested itself whether roots, by virtue of their acid sap, may not, 

 either directly take up, or at any rate attack and liberate for further 

 change, the otherwise insoluble organic nitrogen of the sub-soil ? 



Accordingly, in the autumn of 1885, specimens of the deep, strong, 

 fleshy root of the Medicago saliva were collected and examined ; when 

 it was found that the sap was very strongly acid. The degree of 

 acidity of the juice was determined ; and attempts were made so to 

 free the extract from nitrogenous bodies as to render it available for 

 determining whether or not it would attack and take up the nitrogen 

 of the raw clay sub-soil. Hitherto, however, these attempts have been 

 unsuccessful. But it may be of interest to state, as indicating the 

 extent of the command of the sub-soil which such plants acquire, that, 

 of the 3 plants collected, the roots of one had four branches, respec- 

 tively, 6 feet 4J inches, 5 feet 10| inches, 3 feet 6J inches, and 2 feet 

 9J inches, in length ; the second had two branches 4 feet 10, and 2 

 feet 2 inches, long ; and the third two branches 3 feet 9, and 1 foot 9 

 inches, in length. 



ACTION OF DILUTE ORGANIC ACID SOLUTIONS ON THE NITROGEN 

 OF SOILS AND SUB-SOILS. 



Experiments were next made to determine the action on soils and 

 sub-soils, of various organic acids, in solutions of a degree of acidity 

 either approximately the same as that of the Medicago saliva root-juice, 

 or having a known relation to it. These experiments and their results 

 have been fully detailed elsewhere, and only their general indications 

 can be referred to here. 



Obviously, however, the conditions of experiments in which an acid 

 solution is agitated with a quantity of soil in a bottle, are not 

 comparable with those of the action of living roots on the soil. The 

 root action would necessarily affect only a very small proportion of the 

 total soil. But the results showed, that the more nitrogen was taken 

 up the greater the acidity of the solution, and the question arises, 



F 



