THE SOURCES OF THE HITEOGEN 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 efrdence 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 
acthity of the \dtal force, long after the demands of the organism had begun to require 
more available Nitrogen than was at its disposal. AVhen it is considered how great was 
the length of time during which the gronnng 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 Graminaceae 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 thefr bearings on the main question to those of 1867 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 -u-ithout 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 wfith that of the seed sown, and looking to the proportions of Nitrogen 
iu 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 wfith the Graminacece grown wfithout 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. 617 et seq.). 
It wall be remembered that, in experimenting with Graminacese, 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 wfith 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 Graminaceae 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. 
