262 APPENDIX TO PART I. 



one hand, and to the stem of the branch on the other. In 

 this manner, when the jar came to be placed over them, 

 and to dip beneath the surface of the mercury, the external 

 air was as effectually excluded, as when the whole of the 

 plant had been enclosed. 



'*The results of several experiments conducted after 

 this plan are given in a tabular form in the Memoir ; but 

 it may be sufficient here to specify one of the most satis- 

 factory of those undertaken. In this case the jar itself 

 contained about 600 cubic inches of air, and the plant ex- 

 perimented on was the common lilac {syringa vulgaris). 

 The proportion of carbonic acid in the jar was each morn- 

 ing made equivalent to five or six per cent, by additions 

 through the tube. 



*'The first day no great alteration in the air was detect- 

 ed, but on the second day, by eight in the evening, the 

 oxygen had risen to ^6'5 per cent. In the morning it had 

 sunk to 26 0, but by two P. M, it had again risen to no less 

 than 29'75, and by sunset it had reached 300 per cent. At 

 night it sunk one half per cent. ; but the effect during the 

 following day was not estimated, as the sickly appearance 

 which the plant now began to assume induced me to sus- 

 pend the experiment. 



''In a second trial, however, the branch of a healthy 

 lilac growing in the garden was introduced into the same 

 jar, where it was suffered to remain until its leaves became 

 entirely withered. 



"The first day the increase of oxygen in the jar was no 

 more than 025 per cent., but on the second it rose to 25*0. 

 At night it sunk to nearly 22*0 per cent., but the next 

 evening it had again risen to 27 0. This was the maximum 

 of its increase, for at night it sunk to 26 0. and in the 

 morning exhibited signs of incipient decay. Accordingly 

 in the evening the oxygen amounted only to 26*5 ; the 

 next evening to 255 ; the following one to 24-75 ; and the 

 one next succeeding it had fallen to the point at which it 

 stood at the commencement, or to 21-0 per cent. 



*'The reason of this decrease was, however, very mani- 

 fest from the decay and falling off of the leaves ; so that 

 this circumstance does not invalidate the conclusion which 

 the preceding experiments concur in establishing, namely, 

 that in fine weather a plant, so long at least as it continues 

 healthy, adds considerably to the oxygen of the air when 

 carbonic acid is freely supplied. 



*' In the last instance quoted, the exposed surface of all 



