206 Proceedings of Societies. 



mospheric air. The plants subjected to the former mode of trial were, Bras- 

 sica oleracea, Salicornia herbacea, Pucus digitatus, Tussilago hybrida, Cochlea- 

 ria armorica, Mentha viridis, Rheum rhaponticum, Allium ursinum, and several 

 species of Gramiueae. 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 

 theirchemical 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, cseteris 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 Algae 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 and Optical Struc- 

 ture of the Crystalline Lenses of animals." The author has examined the struc- 

 ture of the crystalbne lens of the eye of a great variety of animals belonging to 



