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60 REPORT—1849. avi % 
carbonic acid upon plants, whether it were suddenly or gradually introduced ; 
for when I exposed the same ferns to air into which 20 per cent. of carbonic 
acid had been added all at once, it was not till the 9th day that any change 
in their appearance was perceptible, and then only in three of the specimens ; 
Pteris serrulata and Adiantum cuneatum being scarcely, if at all affected. - 
However, on the 16th day the influence of the gas was manifest upon all 
except Pteris serrulata; the per-centage of carbonic acid was found to exceed 
that which had been added from without, and the condition of the ferns ge- 
nerally was rather more unhealthy and faded than it had been in the fore- 
going experiment, where the gas had been added in successive doses*. 
So much for this part of the investigation, which seems to be in a manner 
prefatory to the one which may be regarded as the more immediate object 
aimed at by the Association in suggesting these researches, that being, whether 
a larger amount of carbonic acid than is present in our atmosphere would 
increase the vigour, and stimulate the growth, of the tribes of plants which 
are most connected with the fossil remains found in the coal formation. 
With reference to this latter question, Iam not so far advanced towards its 
determination as might have been desired. : 
During the last five weeks Ferns and Lycopodiums have been living in an 
atmosphere containing constantly 5 per cent. of carbonic acid, whilst corre- 
sponding specimens have been placed under similar circumstances, except that 
the abnormal amount of carbonic acid above stated was absent from the air 
of the jar. In both instances the Lycopodiums continue up to this time in 
perfect health, but it must be confessed that the Adiantum cuneatum and fia- 
gelliforme which have been subjected to carbonic acid appear less thriving 
than the corresponding plants not so treated. 
It must be remarked moreover, that the per-centage of gas within the former 
jar has been increased to 5} per cent., the additional 3 per cent. being attri- 
butable to the diseased state of some of the fronds. 
The experiment however shall be continued for a longer period until more 
decisive results have been arrived at. 
But supposing it to be ascertained that ferns will exist in air containing 
5 per cent. of carbonic acid, it still remained a question, whether the animals 
that lived at the same period could have resisted the poisonous influence of 
so large a proportion of this gas. 
In the coal formation, properly so called, Mollusca and Fish appear to be 
the animal remains principally detected, and the difference between the struc- 
ture of existing species, and of those which were in being at so remote a 
period as the one alluded to, may be urged, as an objection to the idea of. 
extending to the latter any inferences that might be deduced from experiments 
instituted upon the former. ; 
Nevertheless as in so fundamental a function as that of respiration, a si- 
milar law pervades all the individuals belonging to the same great natural 
group at the present time, as for instance, what is true in this respect con- — 
cerning the lowest in the scale of Mammalia, holds good likewise with cer- 
tain modifications with regard to the highest, it may not be illogical to presume, 
that the difference as to time would not create any radical change in the re- 
lations of a particular class of animals to carbonic acid, and in their suscep- 
tibility to its influence. 
* I do not find that ferns suffer from confinement in large jars; and at all events, as the 
circumstances were precisely the same in the two cases, with the exception of the presence 
or absence of this excess of carbonic acid, the difference in the appearance of the specimens 
seems clearly referable to the latter cause alone. 
