365 



mine whether the change of colour in the chromule is to be ascribed 

 to this agent. The third object of his inquiries was the source of 

 the irritability 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 ac- 

 tion of the less luminous rays, notwithstanding their chemical influ- 

 ence, 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, Helian- 

 thuses, 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. c ceteris 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 dif- 

 ferent circumstances, by the roots of plants, and chiefly of the He- 

 lianthus animus, Sasittaria sagittifolia, and the Vine. From the ge- 

 neral 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 author found that the 

 most intense artificial light that he could obtain from incandescent 

 lime produced no sensible effect on plants. 



The latter part of the paper is occupied by details of the experi- 

 ments which the author made with a view to ascertain the action of 

 plants upon the atmosphere, 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 be- 

 tween the carbonic acid absorbed, and the oxygen evolved. 



His experiments appear to show that at least 18 percent, of oxy- 

 gen may be added to the air confined in a jar by the influence of a 

 plant contained within 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 per- 

 formed both in dicotyledonous and in monocotyledonous plants, in 

 evergreens as well as in those that are deciduous, in terrestrial and 

 in aquatic plants, in the green parts of eculents as well as in ordi- 

 nary leaves, in Algae and in Ferns as well as in Phanerogamous 

 families. Professor Marcet has shown that it does not take place 

 in Fungi. 



The reading of a paper, entitled, " On the Anatomical and Optical 

 Structure of the Crystalline Lenses of Animals, being the continua- 

 tion of the paper published in the Philosophical Transactions for 

 1833." By Sir David Brewster, K.H., LL.D., F.R.S.,— was com- 

 menced. 



