After I had written, in conjunction with my friend Mr. Allen, the papers which were published in the Philosophical Transactions for 1808,1809 and 1829, on the Respiration of Man, the Graminivorous Animals and Birds, showing the deterioration of the atmospheric air by the quantity of carbonic acid gas produced, I instituted a series of experiments on the respiration of plants, and particularly of their leaves. The difficulty of obtaining, for this purpose, specimens which had been previously accustomed to respire constantly under a glass inclosure, and to maintain all their functions in that situation, was overcome by my obtaining possession of a few fine specimens of fig- and vine-trees, which had been under glass culture for a number of years. To obviate the errors which might arise from making the experiments over water, the apparatus which I formerly used in the combustion of the diamond and other carbonaceous substances was employed, and a modification of the mercurial gaso­meters, with an appendage consisting of a pair of concave glasses, which formed, when united, an oblate spheroid, was found most useful in the investigation of the nature and chemical composition of the atmospheric air which had served the pur­pose, first of animal, and then of vegetable respiration.