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 Graminacee 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- 
