THE SOURCES OE THE XITROGEN OF VEGETATION, ETC. 525 



But, apart from the physiological points just referred to, as already said, this great 

 development of a part of the plant requiring a minimum amount of Nitrogen affords 

 strong evidence of its inability to assimilate free Nitrogen within the range of develop- 

 ment possible when no combined Nitrogen is provided beyond that contained in the 

 original seed. It exhibits the great tenacity of growth of the plant, and shows the 

 activity of the vital force, long after the demands of the organism had begun to require 

 more available Nitrogen than was at its disposal. When it is considered how great was 

 the length of time during which the growing cells were exposed to the conditions in 

 question, there would seem to be a combination of circumstances favourable to the 

 exercise of any force tending to bring free Nitrogen into the constitution of the plant. 

 But no such effect is manifested in the results. 



The Graminacea? referred to in the Table (XII.) under the Title of "1858, A.," and 

 which were grown in the enclosing apparatus of M. G. Ville, as already alluded to, give 

 results quite similar in their bearings on the main question to those of 1857 and 1858 

 already discussed. Being sown later, however, and their period of growth being shorter, 

 they did not manifest such an extraordinary development of root ; nor was there so 

 large an amount of vegetable matter produced. Unfortunately the barley grown in 

 M. Ville's Case without artificial supply of combined Nitrogen, was lost by the giving 

 way of the tube in the combustion for the determination of Nitrogen. In its case, 

 therefore, we can only give the amount of the dry matter of the plants produced. But, 

 comparing this with that of the seed sown, and looking to the proportions of Nitrogen 

 in the produce of barley in the other cases, there is no reason to believe that the result 

 would have formed any exception to that indicated in the other experiments. 



In concluding our remarks on the results with the Graminacese grown without any 

 further supply of combined Nitrogen than that contained in the seed sown, we would 

 beg to refer the reader to the foregoing consideration of the conditions possibly favour- 

 able to the assimilation of free Nitrogen (p. 517 et seq.). 



It will be remembered that, in experimenting with Graminaceae, including some of the 

 same description as those experimented upon by ourselves, M. Boussingault and 

 M. G. Ville obtained most unaccountably discordant results. It will be seen that our 

 own results, from nine experiments with such plants, go to confirm those of M. Boussin- 

 gault. In fact, so far as our labours with these plants bear upon their experiments, 

 they could not have given a more decided result. 



For representations of some of the GraminaceaB grown without any supply of com- 

 bined Nitrogen beyond that contained in the original seed, see figs. 1 to 6, Plate XV. 



Leguminous Plants. 



It still remains to consider the results of our experiments with Leguminous plants 



grown under similar conditions to those of the Graminaceous ones above discussed, and to 



see how far they serve to explain the known characteristics of such plants when grown in 



practical agriculture, to which attention has been directed in Part First of this Paper. 



