Sources of Nitrogen in Plants. 339 
root in such a manner that local hypertrophy is brought 
about, attended with concentration of food-materials, and 
other signs of extraordinarily active metabolism ; and (2) the 
root-hairs are by no means absent, but on the contrary are 
very numerous and well developed. 
Consequently, those who are inclined to compare all the 
cases of symbiosis between roots and fungi, will at least be 
impelled to sharply discriminate between this form and that 
of the Cupuliferae and similar ones. Of course, this dis- 
tinction implies much more. It is at least clear that the 
fungus-hyphae in the leguminous plant do not prevent the 
root-hairs from acting as the absorbing organs, or dissolving 
food substances, & c. for the plant. 
The view to which my experiments and observations on 
the root-tubercles of the Leguminosae lead is the following : 
that the stimulating action of the fungus enables the roots 
to acquire relatively large quantities of nitrogenous materials 
from the soil. I purposely avoided raising the question as 
to whether or not the fungus of the bean-root tubercles 
affects directly the supplies or preparation of nitrogenous 
matter in the soil. We may now, however, survey shortly 
some of the suggestions that have been literally flung about 
lately as to the possibilities of the case under investigation, 
or of others like it. 
First, however, let it be clearly stated that the questions 
raised do not affect the results obtained by Boussingault 
and Lawes, Gilbert and Pugh, as to the non-assimilation of free 
nitrogen by the higher plants. Plants have no power of di- 
rectly employing the nitrogen absorbed by their leaves, &c. 
But it has become a revived question of late as to whether 
the acknowledged sources of nitrogenous food of plants really 
suffice for the large crops taken from the soil, and whether 
the free nitrogen of the atmosphere is not perhaps ‘fixed’ 
in the soil and enabled to combine with other elements and 
so enrich the soil with nitrogen. The importance of the 
subject needs no insisting on, and it may simply be mentioned 
that the Leguminosae especially have repeatedly been cited 
