206 Proceedings of Societies. 
mospheric air. The plants subjected to the former mode of trial were, Bras- 
sica oleracea, Salicornia herbacea, Fucus digitatus, Tussilago hybrida, Cochlea- 
ria armorica, Mentha viridis, Rheum rhaponticum, Allium ursinum, and several 
species of Graminese. Geraniums were the only plants subjected to experiment 
while surrounded with atmospheric air. Comparative trials were made of the 
action on these plants of various kinds of coloured light, transmitted through 
tinted glass, of which the relative calorific, illuminating, and chemical powers 
had been previously ascertained ; and the results of all the experiments are re- 
corded in tables ; but no general conclusion is deduced from them by the author. 
He next describes a few experiments which he made on beans, with a view to 
ascertain the influence of light on the secretion of the green matter of the leaves, 
or rather to determine whether the change of colour in the chromule is to be as- 
cribed to this agent. The third object of his inquiries was the source of the ir- 
ritability of the Mimosa pudica, from which it appeared that light of a certain 
intensity is necessary for the maintenance of the .healthy functions of this plant, 
and that when subjected to the action of the less luminous rays, notwithstanding 
their chemical influence, the plant lost its irritability quite as soon as when light was 
altogether excluded. He then examines the action of light in causing exhalation of 
moisture from the leaves ; selecting Dahlias, Helianthi, Tree Mallows, &c. as 
the subjects of experiment. The general tendency of the results obtained in 
this series is to show that the exhalation is, caeteris paribus, most abundant in 
proportion to the intensity of the light received by the plant. He also made 
various comparative trials of the quantity of water absorbed, under different cir- 
cumstances, by the roots of plants, and chiefly of the Helianthus annuus, Sagit- 
taria sagittifolia, and the Vine. From the general tenor of the results of these 
and the preceding experiments, he is inclined to infer that both the exhalation 
and the absorption of moisture in plants, as far as they depend on the influence 
of light, are affected in the greatest degree by the most luminous rays ; that all 
the functions of the vegetable economy which are owing to the presence of this 
agent, follow, in this respect, the same law; and that in the vegetable, as well as in 
the animal kingdom, light acts in the character of a specific stimulus. The au- 
thor found that the most intense artificial light that he could obtain from incan- 
descent lime produced no sensible effect on plants. 
" The latter part of the paper is occupied by details of the experiments which 
the author made with a view to ascertain the action of plants upon the atmo- 
sphere, and more especially to determine the proportion that exists between the 
effects attributable to their action during the night and during the day ; and also 
the proportion between the carbonic acid absorbed, and the oxygen evolved. 
" His experiments appear to show that at least 18 per cent, of oxygen may 
be added to the air confined in a jar by the influence of a plant contained with- 
in it. He also infers that the stage of vegetable life at which the function of 
purifying the air ceases, is that in which leaves cease to exist. The author 
shows that this function is performed both in dicotyledonous and in monocoty- 
ledonous plants, in evergreens as well as in those that are deciduous, in terres- 
trial and in aquatic plants, in the green parts of esculents as well as in ordi- 
nary leaves, in Algee and in Ferns as well as in Phanerogamous families. Pro- 
fessor Marcet has shown that it does not take place in Fungi. 
Jan. 21 Sir David Brewster's paper, " On the Anatomical arid Optical Struc- 
ture of the Crystalline Lenses of animals." The author has examined the struc- 
ture of the crystalline lens of the eye of a great variety of animals belonging to 
