106 
SIR J. B. LAWES AND PROFESSOR J. H. GILBERT OX THE 
soil, there is nor evidence of coincident and corresponding restoration of nitrogen from 
the free to the combined state. 
In the case of agricultural production for sale, without restoration by manure from 
external sources, a very important condition of the maintenance of the amount of 
nitrogen in the surface soil, or of the diminished exhaustion of it, is the growth of 
plants of various range and character of roots, and especially of leguminous crops. 
Such plants, by their crop-residue, eniich the surface soil in nitrogen. It is, as a rale, 
those of the most powerful root-development that take up the most nitrogen from 
somewhere; and this fact points to a subsoil source. But independently of this, 
which obviously might be held to be only evidence of the necessity of obtaining water 
and mineral matters from below, in amount commensurate with the capability of 
acquiring nitrogen from the air, the experimental results recorded in this paper can 
leave little doubt that such plants obtain at any rate much of their nitrogen from the 
subsoil. The question remains—whether or not the whole of it is derived from the 
soil and subsoil ? At present it is not proved that it is. It is equally not yet 
conclusively proved that it comes from the atmosphere. It may be safely affirmed 
that, in the case of our gramineous, our cruciferous, our chenopodiaceous, and our 
solaneous crops, atmospheric nitrogen is not the source. If, therefore, it should be 
proved to be the source in the case of the Leguminosse, it may be that the development 
of the organisms capable of bringing free nitrogen into combination within the soil is 
favoured by leguminous growth and crop-residue, as there can be little doubt is the 
case with those which induce nitrification. 
Bearing in mind, however, the very large store of already existing combined 
nitrogen, especially in subsoils, it is obviously important to consider, in what way, or 
in what degree, this store may contribute to chlorophyllous vegetation ? 
There is in the first place the question, whether the roots of some plants, and 
especially those of certain deep and powerfully rooting Leguminosse, whose root-sap is 
strongly acid, may either directly take up organic nitrogen from the soil and subsoil, 
or may attack and liberate it for further change, the nitrogen so becoming more 
available. 
Again, so far as is known, the Fungi generally, derive their nitrogen largely, if not 
exclusively, from organic nitrogen. In the case of those of fairy rings for example, 
there can be no doubt that they take up from the soil organic nitrogen which is not 
available to the meadow plants, and that, on their decay, their nitrogen becomes 
available to the associated herbage. In the case of the fungus-mantle observed by 
Frank on the roots of certain trees, it is to be supposed that the fungus takes up 
organic nitrogen, and so becomes the medium of the supply of the soil-nitrogen to the 
tree. More pertinent still, is the action of the nitrifying organisms in rendering the 
organic nitrogen of the soil and subsoil available to the higher plants. It may well be 
supposed, therefore, that there may be other cases in which lower organisms bring the 
