494 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
to plants as ammonia; and hence, if we were to admit that Nitrogen can be oxidated 
into nitric acid in the plant, we must suppose, as in the case of carbon, that there are 
conditions under which the oxygen compound of Nitrogen is reduced within the 
organism, and that there are others in which the reverse action, namely, the oxidation 
of Nitrogen, can take place. In relation to this question, it may be mentioned that 
several specimens of green Wheat and Grass which had been liberally manured with 
nitrates were examined for nitric acid, but no trace of it was found in them. 
7. To the foregoing six conclusions, another may be here added relating to this sub- 
ject, though deduced from the results of experiments on the decomposition of organic 
matter, which will be referred to more fully presently (p. 509 e¢ seg.). So great is the 
reducing power of certain carbon-compounds of vegetable substances, that when the 
vital (growing) process has ceased, and all the free oxygen in the cells has been con- 
sumed, in the formation of carbonic acid, water is decomposed, and hydrogen is evolved. 
This process does not, however, continue long, showing that the cell provides a certain 
amount of matter more easily oxidized than the remainder, or that the entire cell- 
matter, after becoming slightly oxidized, loses its energetic reducing-power. The former 
alternative is the more probable one. 
The foregoing considerations with regard to the intensity of the reducing action of 
certain of the carbon-compounds in plants suggest the idea of a possible source of Ozone, 
very analogous to that by which it is ordinarily obtained by means of phosphorus. As 
is well known, the process consists in allowing oxygen to come into incomplete or only 
instantaneous contact with phosphorus. This substance having an intense avidity for 
oxygen, a part of the latter unites with it to form an oxygen-compound of phosphorus, 
when, if the contact be not too long, another part passes off in the state of Ozone. 
Certain carbon-compounds of the vegetable cell have also a great affinity for oxygen in 
the dark (p. 488); and the oscillations of the affinities, due to the degree of light (pages 
489-492), and to the depth of the cell (p. 493), would afford conditions of molecular 
action somewhat similar to those under which Ozone is produced in the presence of phos- 
phorus. According to this analogy the Ozone would be due to the action of the carbon- 
compounds of the cell on the common oxygen eliminated from carbonic acid by sun- 
light, and not to the direct action of the sunlight itself. The Ozone thus formed, if not 
instantly evolved from the plant, would be destroyed by the easily oxidizable carbon- 
compounds present. It is more probable, however, that the Ozone, stated by Dz Luca 
and others to be observable in the vicinity of vegetation, is due to the intense action of 
the oxygen of the air upon the minute quantities of volatile hydrocarbons emitted 
by the plants, and to which they owe their peculiar odours, than to any action going 
on within the cells. The rapidity of the oxidation in the air of the hydrocarbons, 
and the volatile principles of plants generally, goes to favour the view here suggested ; 
so also does the fact, that Ozone has been observed most readily in the vicinity of such 
plants as are known to emit freely essential oils—as, for instance, those of the Labiate 
family. 
