INFLUENCE OF CARBONIC ACID GAS ON HEALTH OF PLANTS, 57 
rested upon a smooth slate table, having two circular holes perforated in it, 
into each of which a pan or pot containing the plants to be experimented 
upon was inserted. ; 
By the aid of this apparatus I carried on a series of experiments both on 
flowering plants and on ferns, from which I inferred that the one as well as 
the other would continue for a fortnight at least unaffected by a dose of car- 
bonie acid, bearing a proportion to the whole volume of air equal to from 
5 to 10 per cent., but that 20 per cent. would prove injurious to the one, as 
well as to the other, in the course of two or three days. These results were 
however not offered to the Association at Swansea with any confidence, because 
the apparatus contrived for the purpose of carrying them on turned out to 
be defective, the difficulty of cementing the vessels containing the plants to 
the slate table, so as to render the apparatus impervious to air, being such, 
that a large supply of gas was each day found requisite, in order to keep up 
the per-centage to the intended amount. Hence it was probable that during 
a portion of the time the real quantity of carbonic acid in the jar might have 
fallen very short of that with which it was proposed to operate. 
I therefore renewed the experiments in the spring and summer of the pre- 
sent year 1849, in two ways, either of which had been ascertained by previous 
trials to preclude in a great degree the danger of leakage, and thus to render 
the amount of carbonic acid present whilst the experiment was being carried 
on, tolerably constant. 
The first was that of allowing the jars, the edges of which had been well 
ground, to rest upon the surface of a solid and smooth slate table, greased 
along the line of its contact with the glass; the other to make them dip into 
shallow iron dishes with double rims, containing water to the depth of an inch, 
so that the air of the jar might be cut off from the external atmosphere. In 
neither of these cases was there a sufficient loss of gas to interfere with the 
results; in the former, the transmission of air between the smooth surfaces 
of the slate table and the jar being inconsiderable, and in the latter, the quan- 
tity of gas carried off by solution in the water being much reduced, when the 
latter was covered with a thin pellicle of oil. Whatever indeed might be the 
loss in either case sustained, I took care to supply it, by introducing the 
requisite quantity once every twenty-four hours into the jars which contained 
the plants. 
I am therefore now able to offer to the Association, with rather greater 
confidence than before, the following results, as confirmatory of those which 
were stated verbally in my Report, but which, for the reasons already assigned, 
were not published in the Transactions of the Association for last year. 
May 14th.—In the first experiment, five healthy ferns, named Nephrodium 
molle, Adiantum cuneatum, Gymnogramma chrysophylla, and two species of 
Pieris, viz. longifolia and serrulata, were introduced into jar 1 standing in 
_ water, and a quantity of carbonic acid gas was admitted, which equaled 5 
per cent. of the whole amount of air present in the jar. No perceptible change 
Occurring, the quantity was increased on the 17th to 10 per cent., and this 
amount was maintained, as nearly as possible to the same point, by occasional 
additions of the gas, till May 27th. 
_ At the expiration of ten days there was no perceptible difference in the ap- 
pearance of the ferns, either with reference to their preceding condition, or 
_ by comparison with that of five similar ferns, which had been kept for the 
‘Same time under the corresponding glass, without any admixture of carbonic 
acid gas. The experiment was then continued till June 21st, so that the plants 
were exposed to the influence of carbonic acid gas in all for a period of thirty 

