42 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



whether the root action would not effect more resolution on the surfaces 

 actually attacked. Indeed, this must necessarily be the case, if such an 

 action is really quantitatively an important source of the nitrogen 

 taken up by deep and strong rooting plants, with strongly acid-sap. 

 In illustration of this necessity it may be stated that, even if as much 

 as 20 parts of nitrogen were taken up per million of soil, as was 

 the case in some of the experiments, this would only represent 600 Ibs. 

 of nitrogen per acre to the depth examined, namely, 108 inches. 



Upon the whole, the experiments on the action of weak organic 

 acid solutions on raw clay sub-soil, did not give results from which any 

 very definite conclusions can be drawn, as to the probability that the 

 action of roots on the soil, by virtue of their acid sap, is quantitatively 

 an important source of the nitrogen of plants having an extended 

 development of roots, of which the sap is strongly acid. 



That roots do attack certain mineral substances by virtue of their 

 acid-sap, was established by Sachs. It was to carbonic acid that he 

 attributed the action ; but there seems no reason to suppose that other 

 acids in the root-sap may not exert a similar action. The published 

 results of Sachs and others have, however, reference only to the taking 

 up of mineral substances from the soil by virtue of such an action ; 

 and the possibility or probability that the nitrogen of the soil or 

 sub-soil is so taken up, has, I believe, not been considered. 



As bearing on the point, it may be stated that Dr. G. Loges and 

 M.M. Berthelot and Andre, by extracting rich soils by strong hydro- 

 chloric acid, have found that soluble amides are obtained. Supposing 

 the acid root-sap so to act on the insoluble organic nitrogen of the soil, 

 and especially of the sub-soil, the question would still remain whether 

 the amide rendered soluble is taken up by the plant as such, as seems 

 to be probable in the case of the fungi, or whether it undergoes 

 further change into ammonia or nitric acid before serving as food 

 for the plants ? 



The first point to consider is, then, whether chlorophyllous plants 

 can take up amide-bodies and assimilate their nitrogen ? 



Many vegetation experiments have been made to determine this 

 point. In the case of experiments in which soil was used as a matrix, 

 it seemed probable that the amide-body suffered change before becoming 

 available as a source of nitrogen. In the case of some water-culture 

 experiments, however, it was concluded that the amide-body was taken 

 up by the plant as such, and contributed directly as a source of nitrogen 

 to it. It would seem not improbable, therefore, that they might take 

 up directly, and utilize, amide-bodies rendered soluble within the soil 

 by the action of their acid root-sap. 



As a portion of the nitrogen of the soil, when acted upon by acids, 

 is liberated as ammonia, it is a question whether this will be either wholly, 

 or partially, nitrified, before being taken up by the plant. Obviously, 

 too, if the portion brought into the condition of soluble amide, be not 

 taken up as such, it also will be subject to further change ; perhaps 

 first into ammonia, and then into nitric acid. But, on such a supposition, 



