QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
91 
an enormous store of already combined nitrogen, was susceptible of nitrification, 
provided the organisms are present, and the supply of oxygen is sufficient, the 
results did not indicate that these conditions would be adequately available 
in such cases as those of the very large accumulations of nitrogen by the Medicayo 
saliva for a number of years in succession on the clover-exhausted land, or by the red 
clover on the bean-exhausted land. 
The question arose—whether roots, by vmtue of their acid sap, might not, either 
directly take up, or at any rate attack and liberate for further change, the otherwise 
insoluble organic nitrogen of the subsoil ? Accordingly, specimens of the deep, strong, 
fleshy root, of the Medicayo saliva were collected and examined, when it was found 
that the sap was very strongly acid. The degree of acidity was determined, and 
attempts were made so to free the extract from nitrogen so as to render it available 
for determining whether or not it would attack and take up the nitrogen of the raw 
clay subsoil. Hitherto, however, these attempts have been unsuccessful. 
When this difficulty arose, it was decided in the meantime to examme the action 
on soils and subsoils, of various organic acids, in solutions of a degree of acidity 
either approximately the same as that of the lucerne root-juice, or having a known 
relation to it. 
It was found that the weak organic acid solutions did take up some nitrogen from 
the raw clay subsoil, and more from the poor lucerne surface soil. But when solutions 
of only approximately the acidity of the root-sap were agitated with an amount of 
soil which it was thought would be sufficient to yield so much nitrogen as to insure 
accurate determination, it was found that the acid frequently became neutralised by 
the bases of the soil, and that less nitrogen remained dissolved after a contact of 
24 hours, or more, than after only 1 hour. The strength of the acid liquids was 
therefore increased, and the relation of soil to acid diminished. More nitrogen was 
then taken uj), and more after the longer than after the shorter period of contact. 
Still, on adding fresh acid solution to the already once extracted soil, a limit to the 
amount of nitrogen rendered soluble was soon reached. 
Here again, the conditions of experiment in the laboratory are not comparable with 
those of the action of living roots on the soil, and the results obtained did not justify 
any very definite conclusion as to whether the action of the roots on the soil, by 
virtue of their acid sap, is quantitatively an important source of the nitrogen of 
plants having an extended development of roots, of which the sap is strongly acid. 
Dr. G. Loges has published the results of experiments in which he acted upon 
soils by pretty strong hydrochloric acid, and determined the amount of nitrogen taken 
up. One of his soils contained, however, 0’804, and the other 0‘367, per cent, of 
nitrogen; whilst the surface soil of the lucerne plot at Bothamsted contained only 
about 0T25, and the subsoil, which is assumed to have yielded large quantities of 
nitrogen to the crops, little more than 0'04 per cent. Again, in the one case Loges 
found 40 per cent., and in the other 22'6 per cent., of the total nitrogen taken up. 
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