446 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
A bean and a wheat crop may yield equal amounts of dry matter per acre, whilst the bean 
produce would contain from two to three times as much Nitrogen as the wheat. Never- 
theless some attempts at approximate measurement have indicated that the wheat-plant 
offers a greater external superficies in relation to a given weight of dry substance, than 
does the bean. The wheat-plant would, of course, show a still higher relation of super- 
ficies to a given amount of Nitrogen fixed. If, therefore, the larger amount of Nitro- 
gen yielded per acre by a bean than by a wheat crop be due to a larger assumption of 
it directly from atmospheric sources in some form, it is obvious that the result must be 
due to character, and function, and not to mere extent of surface above ground. In 
connexion with this point it may be observed, more particularly with reference to the 
crops that are grown for their ripened seed, that the Leguminous ones generally main- 
tain their green and succulent surface in relation to a more extended period of the 
season of active growth and accumulation than do the Graminaceous ones. 
(7) Assimilation of free or uncombined Nitrogen by Plants.—It has been seen, in the 
course of the foregoing brief review of the various sources of combined Nitrogen to 
plants, that those of them which have as yet been quantitatively estimated are inade- 
quate to account for the amounts of Nitrogen obtained in the annual produce of a given 
area of land beyond that which may be attributable to the supplies by previous manuring. 
It must be admitted, too, that the sources of combined Nitrogen which have been alluded 
to as not yet even approximately estimated in a quantitative sense (if indeed they are all 
fully established qualitatively) offer many practical difficulties in the way of any such 
investigation of them as would afford results directly applicable to our present purpose. 
It appeared, therefore, that it would be desirable to settle the question, whether or 
not that vast storehouse of Nitrogen, the atmosphere, in which the vegetation which 
covers the Earth’s surface is seen to live and flourish, be of any measurable avail to the 
growing plant, so far as its free or uncombined Nitrogen is concerned. 
The settlement of this question (whether affirmatively or negatively) would at any 
rate indicate the degree of importance to be attached to the remaining open points of 
inquiry. Indeed, were it found that plants generally, or some of those we cultivate 
more than others, were able to fix Nitrogen from that presented to them in the free or 
uncombined form, we should, in this fact, have a clue to the explanation of much that 
is yet clouded in obscurity in connexion with the chemical phenomena of Agricultural 
production. We should establish for vegetation, the attribute of effecting chemical 
combinations with an element at once the most reluctant to associate itself with other 
bodies in obedience to laboratory processes and at the same time apt to rid itself of 
connexions once formed in the most violent manner—as the explosive character of many 
Nitrogen compounds forcibly illustrates. We should further be able, much more satis- 
factorily than we are at present, to account—by processes established to be going on 
under our own observation—for the actually large total amount of combined Nitrogen 
which we know to exist and to circulate, in land and water, in animal and vegetable 
life, and in the atmosphere. 
