QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
39 
ammonia was only found twice tliroughout the summer. Neither nitrates nor nitrites 
were ever found in the solutions. 
Hampe concluded tliat the urea was taken up by the plants as such, and that it 
served as a source of nitrogen to them. This result he considered not inconsistent with 
the view that plants, other than fungi, cannot utilise products of the plant itself, such 
as the alkaloids, which they can no more assimilate as a source of nitrogen, than they 
can sugar as a source of carbon. (Jrea being, on the other hand, a product of the 
degradation of animal substance, there seemed no reason why it should not serve as a 
source of nitrogen to plants. 
In his experiments with ammonia Hampe used the phosphate ; and small and large 
maize were the plants selected. In their early stages the plants seemed to suffer 
rather than to benefit by the ammoniacal supply ; but eventually they gave good 
growth; and produced ripe seeds, which on being re-sown germinated* 
In the experiments with uric acid the same descriptions of maize were employed. 
The solutions were frequently renewed, and in those which were removed ammonia 
was always found, but not uric acid. But even in solutions without a plant the uric 
acid rapidly decomposed. From the results it was concluded that the uric acid had 
served as a source of nitrogen to the plants ; though probably not directly, but by its 
products of decomposition. 
In the case of hippuric acid, applied as hippurate of potash, and to the same 
descriptions of plant, the growth was somewhat dwarf; but seeds, which were found 
to germinate, were produced. Benzoic acid was always found in the solutions after 
vegetation, and also in corresponding solutions without a plant. In both cases a 
mould formed on the surface, but not in the body of the liquid. The question arose 
whether the benzoic acid Was only formed in the solution under the influence of the 
mould acting as a ferment, or whether in part in the plant itself, glycocoll being at 
the same time produced, and serving as the nitrogenous supply ? If the latter were 
the case, the action would be the convrese of that which takes place in the animal, 
when benzoic acid unites with glycocoll, forming hippuric acid, which is eliminated. 
Direct experiments v/ere also made with glycocoll itself. With it, the plants were 
better than in any of the other experiments. At each renewal of the solution, the 
old liquid was examined both for glycocoll and for ammonia. Glycocoll was always 
found, but ammonia only in very small (^[uantity, and its occurrence was apparently 
connected with decomposition of plant-substance. Hampe concluded that glycocoll 
was as available as nitrogenous food to plants as nitric acid. 
In 1868 Dr. P. Wagner (‘Versuchs-Stationen,’ vol. 11, p. 287) made experiments 
in continuation of those by Hampe above described. He repeated, with some modifi¬ 
cations, the experiments with ammonium salts, hippuric acid, and glycin, and also 
experimented with kreatin. 
With ammonium phosphate good growth was obtained. Neither niti’ate nor nitrite 
