QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
41 
sition, as the source of nitrogen. To this end the water-culture method was adopted, 
and rye was the plant selected. 
According to the report, the vegetation went on for more than a year—430 days I 
The amount of the dry substance produced was 3G5 times that of the seed sown ; but 
no seed was developed. Neither ammonia nor nitric acid was found in the solutions. 
But, on boiling, a small quantity of an organic body was deposited. From 4'5 grams 
tyrosin the vegetation acquired O'18 nitrogen, corresponding to 2'3 tyrosin. No 
tyrosin was found in the extract of the stems and leaves, but traces were detected in 
that of the roots. 
W. Wolff concluded that tyrosin suffered change as soon as it entered the plant, 
and that thus the action differed from that found by Hampe in the case of urea. 
He considered that the tyrosin was, at any rate in part, transformed in the solution, 
under the influence of the roots ; but that ammonia was not one of the products of 
the change. If the tyrosin were taken up at all as such by the roots, it did not pass 
unchanged to the upper organs; but when its nitrogen, in whatever form, was 
assimilated by the plant, it was distributed through the various organs, as in the case 
of land plants growing under natural conditions. 
From the various results above quoted it seems at any rate very probable, if not 
absolutely demonstrated, that green-leaved plants can take up soluble complex organic 
bodies, and assimilate their nitrogen, when they are presented to them under such 
conditions as in water-culture experiments. Even under such conditions, however, if 
the nitrogenous substance supplied was readily subject to change in the solution 
itself, it was doubtful whether it was taken up as such, or only after first undergoing 
change ; and it is pretty certain that such substances supplied to the soil, would either 
in great part or entirely suffer change before being taken up by the plant. 
The probability that the higher plants can, under any circumstances, take up 
complex nitrogenous bodies, and appropriate their nitrogen, is of considerable interest 
from a theoretical point of view. But under the ordinary condition of the growth of 
plants in soil, such substances will seldom if ever be available to them, excepting it 
may be under the influence of the action of the root-sap in rendering soluble the 
nitrogenous compounds of the soil and subsoil, which exist in them in an insoluble 
condition. 
It will be of interest next to consider what evidence exists as to other modes in 
which green-leaved plants may acquhe nutriment from compounds existing in an 
insoluble condition in the soil and subsoil. 
Dr. Frank has observed that the feeding roots of certain trees are covered with a 
fungus, the threads of which force themselves between the epidermal cells into the 
root itself, investing the cell, but not penetrating the fibro-vascular tissue. In such 
cases the root itself has no hairs ; but there were similar bodies external to the 
fungus-mantle, which were prolonged into threads among the particles of soil. The 
MDCCCLXXXIX.—B, G 
