248 THE BOTHAMSTED EXPERIMENTS. 



ated from the above-ground parts of the plant into the roots, 

 and possibly some of it passed from them into the soil. 

 Again, the amount of carbonic acid found in the ashes of the 

 crop for 100 of nitrogen in it would require about one and a- 

 half time as much lime as was found in association with it ; 

 indicating the probability that part of the nitrogen taken up 

 as nitric acid was as the nitrate of some other base — potash, 

 and possibly to some extent soda also. 



Turning to the results with the rotation clover grown by 

 the mixed manure, calculation shows that in the case of this 

 continuously vegetating, unripened, and much higher nitrogen- 

 yielding crop, there was very much more of both lime and 

 carbonic acid in the ash for 100 of nitrogen assimilated than 

 in the total bean-crop. If, however, the whole of the nitrogen 

 of the clover crops had been taken up as calcium nitrate, it 

 would have required nearly twice as much lime as the amount 

 found, provided the whole of it remained ; nor would the 

 amounts of potash and soda found suffice to make up the 

 balance. Again, the amount of carbonic acid found is little 

 more than two-thirds as much as would be required to repre- 

 sent organic acid equivalent to the amount of nitric acid 

 subjected to change. Either, therefore, fixed base, partly in 

 combination with organic acid, must have been eliminated 

 from the above-ground parts of the plant, and passed into the 

 roots, and possibly into the soil, or a good deal of the nitro- 

 gen must have been taken up in some other form than as 

 nitrate ; possibly in part as organic nitrogen taken up from 

 the soil by the agency of the acid sap ; or, in part as free 

 nitrogen, probably brought into combination under the in- 

 fluence of micro-organisms within the nodules found on the 

 roots of leguminous plants, the resulting compound being 

 either directly available as a source of nitrogen to the host, or 

 it may be so only after it has itself suffered change. 

 Lime as a However this maybe, considering the very characteristic 

 earner of differences in the mineral composition of the different crops 

 of rotation according to the amounts of nitrogen they assimi- 

 late, the fact that undoubtedly the highly nitrogenous Legum- 

 inosse do take up at any rate a large proportion of their 

 nitrogen as nitrate, and that the greater the amount of nitro- 

 gen assimilated the more is the ash characterised by contain- 

 ing fixed base, and especially lime, in combination with 

 carbonic acid, it seems very probable, if not indeed established, 

 that the office of the lime, and partly that of the other bases 

 also, is that of carriers of nitric acid ; which, when trans- 

 formed, and the nitrogen assimilated, leaves the base as a 

 residue, presumably in combination with organic acid. Fur- 

 ther, the power of these plants to assimilate so very much 



