THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 523 



seed, — the gain appearing only when the Nitrogen in the soil and pot is taken into 

 account. It will be remembered that the results of the experiments on the question 

 whether there was an evolution of Nitrogen during germination and growth (Table XL, 

 p. 513) showed how completely the plants could appropriate the Nitrogen of the seed 

 from which they grew, leaving only traces of it in the soil. Again, the experiments on 

 the decomposition of Nitrogenous organic matter (Tables VIII. and IX., p. 506) have 

 shown how thorough was the decomposition coincident with the passage of any large 

 percentage of the combined Nitrogen of the substance into the soluble state of ammonia. 

 Taking together these facts, we have strong grounds for assuming that at least a part 

 of the Nitrogen found in the soil, in the cases where there was a gain of it in the total 

 products, has never been in actual connexion with the plant at all. Indeed, in view of 

 the facts just referred to, any gain of Nitrogen in connexion with the plant, without 

 there being a larger quantity of Nitrogen in the plant itself than that provided in the 

 seed, would be very questionable evidence upon which to establish the fact of the assi- 

 milation of free Nitrogen. 



But the results obtained with Graminacese in 1858, when all possible sources of error 

 which the experience of the previous year had suggested had been eliminated, point, 

 without exception, to the fact that, under the circumstances of growth to which the plants 

 were subjected, no assimilation of free Nitrogen has taken place. The regular process 

 of cell-formation has gone on ; carbonic acid has been decomposed, and carbon and the 

 elements of water have been transformed into cellulose ; the plants have drawn the nitro- 

 genous compounds from the older cells to perform the mysterious office of the formation 

 of new cells (see Notes on growth, Appendix, pp. 559, 561); those parts have been deve- 

 loped which required the smallest amount of Nitrogen ; and all the stages of growth 

 have been passed through to the formation of glumes, pales, and awns for the seed. 

 In fact, the plants have performed all the functions that it is possible for a plant to 

 perform when deprived of a sufficient supply of combined Nitrogen. They have gone 

 on thus increasing their organic constituents with one constant amount of combined 

 Nitrogen, until the percentage of that element in the vegetable matter is far below the 

 ordinary amount of it — that is, until the composition indicates that further development 

 had ceased for want of a supply of available Nitrogen. 



Throughout all these phases, water saturated with free Nitrogen has been passing 

 through the plant ; nitrogen dissolved in the fluid of the cells has constantly been in 

 the most intimate contact with the contents of the cells and with the cell-walls. The 

 newly forming cell, stunted in its development for want of assimilable Nitrogen, has 

 nevertheless been surrounded by free Nitrogen. Its delicate membranes have been 

 saturated with water, itself saturated with free Nitrogen ; and such are the laws in 

 accordance with which the absorption of gases, and the transmission of liquids through 

 membranes take place, that the instant a part of the Nitrogen of the saturated fluid be- 

 came assimilated, the equilibrium would be restored, by the penetration into the cell of 

 other saturated liquid, and the re-saturation of that from which Nitrogen had been with- 



