26 
REPORT- 1847 * 
the results obtained and described in this and former reports, ^at the de¬ 
composition of the carbonic acitl by plants under the agency of light ^ ‘ 
simple chemical operation, as has been supposed by some, etfected by Uk 
cblorophyl, but the result of an exertion of the vital principle of the growing 
plant, which requires the external stimulus of light to call it into action. 
A great number of experiments have bocn made with the prismatic rays, 
hoping to he enabled to settle a jioint on which an American phihisopbtf 
atid mvself are at issue, this getitlcnian having published results the very 
opposite to those which I have obtained and piiblisbetl. The method pur¬ 
sued has been to place leaves in small tubes filled with water impregnated 
with carbonic acid, and to place thosi* tubi'S across the rays formed by a very 
excellent flint-glass prism. The results have varied with every experiment. 
If we place a small sprig covered with leaves in the tube, wc get the largest 
quantity of gas in one ray; if we remove the leaves from the branch, we 
shall then get the most gas under another ray. No two plants, as far as I 
am aware, give the same quantity of oxygen, in the saini; lime, under tlie io- 
fluence of the same ray, and the age of the {ilatit must materially alter* all 
the efi'ects; the Hjune plant at one age giving evidence of bcijig excited roost 
readily by ibti blue rays, and at another by the yellow or the red rays. Mor^ 
over, I am satisfied that by rerooviog a mtunber, whetlier a branch or a leftf, 
froiu the plant, wo give a shock to the living system, which prevents 
obtaining any n-sult which shall actually represent the true conditions of the 
growing plant. On this point the experiments of Mattcuoci (Cimeiito, Juilld 
et Aoht, 1816) are most satisfactory. 
In all experiments ou plants, it must he borne in mind that we are dealing: 
with an organized body endowed with peculiar vital functions. As these are 
ever liable to dcrangetuent from umnerous causes whicli arc almost beyond 
the reach of our exarainiition, it is only by a great number of cxporinientt 
that anything like an approximation to the truth can be arrived at. Asl 
have pointed out, anything wliich at all interferes with the functional powers 
ot the groiyuig plant, materially altcw all tlio conditions which we are desirous 
ot cxaunnmg; heiico I am perfectly satisfitKl that all the oxperimeuts made 
with ieaves in tubes of water exposed to tlio prismatic rays arc fallacious, and 
do not at all r<>p^nt the powers of the plant to which the loaves belong, 
it IS however evident, from a curtTul comparison of all the results obtained, 
that iighu as uistinguisbed from hmt and aclinisni, is the principle on vliicb 
the secretion of cai-lmn and the evolution of oxvip.mi hv 
r ^ inferred that lighl was oecessary 
from tlK^limriV* I>aubeuy iiowovcr obtained no rtsult 
rdue L^Io I emits a much purer M-hite light. 
imjriucnig also chemical effects in a markid manner. 
‘‘effe;t of'Somn""- of colouring matter of leaves to the 
of S tuiU exhaling oxygen” by the agency 
pos nl it j'* proportion w the dccom- 
kS iVf Lunllcy takes it rriicorv of HorUculture, 
of Yellow I’ichtTn'l ^ published a memoir ‘On the AcUon 
can Jour^ of Plants' &c. (the Ameri- 
he has settled the nZi'in * ^ 1844), in which he contends that 
chlorophyl in leaves^ it J«'* ^*bat the yellow rays produce 
this observer that tiie ®^tementof results as given by 
rver, that the greening was not even iu his experiments confined to 
