528 Mi:. J. I'.. l.\\Vi:s. DB. GILBERT, AM) DB. FTOH OB 



Nitrogen compared with the seed, to plants at the time in a precisely similar DOB- 

 dition to those now under consideration, the increa.se in the rapidity of growth was most 

 marked. 



Most of the buckwheat seed sown came up; but about half of the plants lived for only 

 a few days. The remainder, which survived, went through all the stages of develop- 

 ment to flowering; but the entire amount of growth was on a very limited scale. 



Reference to the last column of Table XII. will show that, under the conditions of 

 growth above described, the buckwheat, like the plants already discussed, indicated 

 no gain of Nitrogen. In fact there appeared to be a loss in the experiment of nearly 

 2 milligrammes of Nitrogen; and that the result should be to a small extent in this 

 direction may, perhaps, be accounted for by the fact of some of the plants dying early, 

 in consequence of which there may have been a slight evolution of free Nitrogen due 

 to decomposition. 



Bearing of the above results on the question of the evolution of free Nitrogen from the 

 Nitrogenous Constituents of plants during growth. 



We have thus far only considered the above results so far as they bear upon the 

 question of the assimilation of free Nitrogen by plants. But from the constancy of the 

 amount of combined Nitrogen maintained in relation to that supplied, throughout the 

 experiments, they afford evidence of an important kind in regard to the converse 

 question of whether plants give off free Nitrogen during growth. With no less force 

 than they point to the absence of any assimilation of free Nitrogen, do these results 

 show that, under the circum stances of growth involved, there has been no evolution 

 of free Nitrogen from the nitrogenous compounds of the growing plant. At all events, 

 the assumption that an evolution of free Nitrogen has taken place implies, as in the 

 case of the experiments discussed at pp. 513, 514, the still more improbable one, that 

 there has been an exactly compensating amount assimilated. But since the conditions 

 of the experiments now under consideration were arranged with special reference to the 

 question of assimilation, they necessarily do not embrace all the circumstances which, 

 a, priori, would be considered the most favourable for the evolution of free Nitrogen 

 during growth. 



Various experimenters, from the time of De Saussure until quite recently, have enter- 

 tained the idea of the probability of the decomposition of nitrogenous compounds, and 

 the concomitant evolution of free Nitrogen, during the growth of plants. We are 

 ourselves engaged in following up the subject, by methods better qualified to settle the 

 question than those adopted in regard to the question of assimilation of Nitrogen. We 

 shall therefore not treat of this subject any further here, than to call attention to the 

 incidental bearing upon it of the results now under consideration. 



The fact that there has been no decomposition of nitrogenous compounds and loss of 

 Nitrogen as the result of growth, in the particular conditions to which these experimental 

 plants were subjected, affords little evidence that no such decomposition could take 



