40 
S[R J. B. LA WES AND PROFESSOR J. H. GILBERT ON THE 
could be found in tlie plant, and it was concluded that, as in Hampe’s experiments, 
the ammonia had served as a supply of nitrogen. 
When ammonium carbonate was used, nitric acid was found both in the solution 
and in the plant; and it was concluded that the ammonia had not served directly as 
a supply of nitrogen. 
In Hampe’s exjDeriments with hippuric acid, it was proved that it served as a 
supply of nitrogen to the plant; but as benzoic acid was found not only in the 
vegetation solution, but in a corresponding solution without a plant, and there was, 
in both cases, fungoid growth on the surface, it was uncertain whether the breaking 
up of the hippuric acid had taken place only externally to the plant, under the 
influence of the fungus acting as a ferment, or also within the plant itself, benzoic 
acid being excreted. By excluding the access of the air, and by frequently passing- 
carbonic acid through the solutions, the formation of the fungus was prevented. 
Benzoic acid was, however, still found in the plant-solution, but not in the solution 
without a plant. 
Wagner concluded that hippuric acid was broken up within the plant itself, 
benzoic acid being excreted, and that it also suffered decomposition in the solution by 
the agency of the fungus. 
Hampe had obtained very good growth with glycin, but Wagner thought it 
desirable to prevent the formation of the mould on the surface of the solution. This 
he succeeded in doing by frequently passing carbonic acid through it, and glycin was 
then easily detected in it. Ammonia was only found when there was some decay of 
the roots. Wagner concluded that the glycin had been taken up by the plant as 
such, and had contributed nitrogen to it. 
Kreatin v/as used as being closely allied to urea, which had been proved to’serve as 
a supply of nitrogen to plants. For some time neither mould, nor ammonia, nor 
smell, was developed in the vegetation-solution ; when they were, it was renewed ; and 
some ammonia again appeared when the roots showed signs of decay. Wagner could 
not detect kreatin in the plant, as Hampe had urea. But from its constant presence 
in the solution, and the very little development of ammonia, he concluded that it 
served as nitrogenous food to the plant as did urea. 
Wagner considered it established that the higher plants can obtain nitrogen from 
complex organic bodies as well as from ammonia and nitrous and nitric acids, and that 
thus the doctrine of the nutrition of plants was much extended. He did not suppose 
that such a source was essential, and whether in the case of plants growing in soil 
such substances would serve as a direct supply would depend on the length of time 
they could remain in such a medium in an undecomposed condition. 
The last experiments of this description to notice are those of W. Wolff with 
tyrosin (‘Versuchs-Statlonen,’ vol. 10, p. 13). He had formerly experimented with 
Knop, on leucine, tyrosin, and glycocoll; and he now repeated the experiment with 
tyrosin, to determine whether it served directly, or only by its products of decompo- 
