332 
MR. PEPYS ON THE RESPIRATION OF THE LEAVES OF PLANTS. 
then passed and repassed occasionally for about three hours, when it was examined, 
and found to contain 4 per cent, carbonic acid. 
The hemispheres were then left open to the two small gasometers during the night, 
and on the morning of the 22nd of April (barometer 30’042, thermometer 61°) the 
air was examined and found to contain 3 per cent, carbonic acid. 
After clearing the gasometer and hemispheres from the remaining respired air, 
by passing a plentiful quantity of atmospheric air through them, I left seventy- 
two cubic inches of atmospheric air (containing seventy nine azote and twenty-one 
oxygen) until the 25th April (barometer 30T10, thermometer 70°). I then passed 
and repassed this air several times, and on examination found no alteration in its 
composition, which, by my eudiometer, was twenty-one parts oxygen and seventy- 
nine azote; but there was found in the hemispheres about 100 grains of pure water, 
which must have transpired from the leaf during this confinement. 
July 25th, 1842. — Barometer 29'950. Thermometer 71°. 
The experiment of the 21st of April last, as to the action of the fig-leaf on the re- 
spired air, was repeated, and on leaving, it contained 4 \ per cent, carbonic acid, which 
on examination next morning was reduced to 2 per cent. 
It will be seen from the preliminary experiments, that particular attention was 
paid to preserve the functions of the leaf in a healthy state, both during its inclosure 
and after its liberation, for in proportion as this essential condition was secured, would 
be our confidence in the accuracy of the results of the future proceedings for deter- 
mining the action of the leaf upon a portion of atmospheric air which had served the 
purpose of respiration. 
The conclusions drawn from the numerous experiments made during a long period 
are, that vegetation, particularly in fine healthy leaves, is always acting to restore the 
atmospheric air to its original composition of twenty-one parts per cent, of oxygen, 
by the absorption of the carbonic acid gas and the liberation of oxygen ; that this 
action is accelerated by the aid of light, but that it continues even during the night, 
although more slowly, and that the production of carbonic acid gas is never observed 
to take place when the leaf is in health. 
The fluid given off during the experiments, when examined, proved to be pure 
water ; when tested by lime water it showed no carbonic acid. 
The power possessed by the leaf of taking up carbonic acid gas seems very ana- 
logous to that by which food is collected by animals ; the first portions of carbonic 
acid are more quickly taken up than the remaining portions, and one might almost 
say, that with plants, as with animals, at first a keen appetite is in operation, which 
being satisfied, is followed by repletion. 
