QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION 
93 
of others, made to determine whether such plants can take up such bodies, and 
assimilate their nitrogen, have been considered. 
Upon the whole it seems probable, that green-leaved plants can take up soluble 
complex nitrogenous organic bodies, when these are presented to them under such 
conditions as in water-culture experiments, and that they can transform them and 
appropriate their nitrogen. If this be the case, it would seem not improbable that 
they could take up directly, and utilise, amide bodies rendered soluble within the soil 
by the action of their acid root-sap. 
In connection with the subject of the conditions under which the insoluble organic 
nitrogen of sods and subsoils may become available to chlorophyllous plants, some 
results of Frank are referred to. He observed that the feeding roots of certain 
trees were covered with a fungus, the threads of which forced themselves between the 
epidermal cells into the root itself, which in such cases had no hairs, but similar bodies 
were found external to the fungus-mantle, which prolonged into threads among the 
particles of soil. Frank concluded that the chlorophyllous tree acquires its sod 
nutriment through the agency of the fungus. 
Such a mode of accumulation by some green-leaved plants, obviously allies them 
in this respect very closely to fungi themselves ; indeed, it is by an action on 
the sod which characterises non-chlorophyllous plants, that the chlorophyllous plant 
acquires its soil-supplies of nutriment. But inasmuch as, in the cases observed, the 
action was most marked in the surface layers of soil rich in humus, and it is stated 
that the development has not been observed on the I'oots of any herbaceous plants, 
the facts so far recorded do not aid us in the explanation of the acquirement of 
nitrogen by deep and strong rooted Leguminosee from raw clay subsods. Still, in view 
of the office within the soil which is by some attributed to micro-organisms, and other 
low forms, the observations are not without interest. 
It is admitted that existing evidence on the various points which have been referred 
to is insufficient to explain the source of the whole of the nitrogen of the Leguminosee. 
The question arises, therefore, whether the free nitrogen of the atmosphere is fixed, 
either by the plant, under the influence of electricity or otherwise, or within the sod, 
by the agency either of electricity or of micro-organisms ? We believe that the 
results of BoussIngault, and those obtained in conjunction with the late Dr. Pugh at 
Bothamsted, are conclusive against the supposition of the fixation of free nitrogen 
by the higher plants, under conditions in which the possibility of electrical action, 
or of the influence of micro-organisms, is excluded. The following is a brief resume 
of the more detailed account and discussion, given in Part II., of the recently 
published results and conclusions of others, from experiments for the most part made 
under such conditions as not to exclude the possibility of the influence of electricity 
or of micro-organisms. 
