TOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 211 



and this has been conceived to arise from the powers of vegetation being destroyed; 

 or in other words, the death of the plant ; and from hence it has been inferred, with 

 some degree of plausibility, not only that the leaves actually retained their vegeta- 

 tive powers for some time after they were separated from their stock, but that it 

 was in consequence of the exertion of these powers, that the air, yielded in the 

 experiment, was produced. 



But I have found, that though the leaves, exposed in water to the action of 

 light, actually do cease to furnish air after a certain time, yet that they regain 

 this power after a short interval, when they furnish (or rather cause the water to 

 furnish) more and better air than at first, which can hardly be accounted for on 

 the supposition that the air is elaborated in the vessels of the plant. 



Exper. 29. A globe, containing 46 cubic inches, filled with fresh spring 

 water and 2 peach leaves, was exposed in the window to the action of the sun's 

 rays, 10 days successively, the weather being in general fine, when the following 

 appearances took place. The 1st and 2d day, a certain quantity of air was pro- 

 duced, about as much as in former like experiments. The 3d day very little 

 was produced ; and the 4th day none at all, the globe to all appearance being 

 quite exhausted. Continuing the experiment however, on the 5th day, the 

 water having acquired a faint greenish hue, air was again produced pretty plen- 

 tifully, making its appearance on the surface of the leaves in the form of air- 

 bubbles, as at the beginning of the experiment ; at the end of the 6th day the 

 air was removed, and it was found to amount to tV^ of a cubic inch, its quality 

 being 232 degrees, or la -f 372 = l68. On the 7th day -^V of a cubic inch of 

 air was produced of 297 degrees, or \a -{■ 3n=. 1.03 ; and during the 8th, Qth, 

 and 10th days. If cubic inch of air, of 307 degrees (or \a -\- An=. I.93), was 

 furnished ; after which an end was put to the experiment. The total quantity of 

 air produced S-fVo- cubic inches ; mean quality 29 1 degrees, or la -|- 3n = I.09. 



Finding that leaves which were dead, or in which all the powers of vegetation 

 were evidently destroyed, continued notwithstanding to separate air from water, 

 and that in so great abundance, I was desirous of seeing the effect of exposing 

 fresh healthy leaves in water which I knew to be previously saturated with, and 

 disposed to yield dephlogisticated air. I conceived, that if the plants exposed in 

 water actually imbibed fixed or phlogisticated air as food, and after digesting it, 

 " discharged the dephlogisticated air as an excrement ;" in that case, as there is 

 no instance of any plant, or animal, being able to nourish itself with its own 

 excrement, the leaves exposed in water saturated with dephlogisticated air, 

 instead of imbibing and elaborating it, would immediately dre. The experi- 

 ments which I made to ascertain this fact, without any comment, were as 

 follow. ' 



Exper. 30. Having provided a quantity of water, which, by being exposed 



£ £ 2 



