222 RECENT RESEARCHES ON THE RESPIRATION OF PLANTS. 



fact, tliat he was induced to neglect as trifling all contrary ap- 

 ])earances ; and this is the more probable as in two instances he 

 noticed its exhalation, without, however, doing more. 



It being clearly ascertained that jilants decompose carbonic 

 acid, and that they also exhale it, we may fiiirly infer that the 

 accumulation of carbon is explained by the predominance of the 

 first process over the second ; and to show that this is so, the 

 following experiments were made. A top of a young, green, 

 and leafy stem of Fagopyrum cymosuni, w^eighing, after the ex- 

 periment, 15 grammes, was placed in the curved part of the 

 apparatus before mentioned, which was then carefully closed and 

 luted ; a small caoutchouc bladder, furnished with a stop-cock, 

 and containing 200 cubic centimetres of carbonic acid, was then 

 fixed to a tube, so that the stop-cock being open there was a 

 free comnmnication between the gas in the bladder and the air 

 in the flask. After an exposure to the sun for six hours, only 

 Yo cubic centimetres of gas were found in the flask and bladder. 

 Whilst this experiment was going on, another, and in every 

 respect similar piece of the same plant, was in a second apparatus 

 with some baryta-water, which fixed 1 1 cubic centimetres of ex- 

 haled gas. 



In order to ascertain whether the air in calm weather can by 

 its carbonic acid supply the wants of a plant, notwithstanding 

 the loss of carbon occasioned by the latter, both by day and 

 night, water saturated with baryta and its carbonate, and with a 

 surface of 300 square centimetres, was exposed for an hour in 

 the open air to the rays of the sun ; the pellicle which had then 

 formed gave, on being decomposed by citric acid, 15 cubic centi- 

 metres of carbonic acid, that is 180 cubic centimetres for twelve 

 hours of day. Now, the surface of the leaves of the 15 granmies 

 of Fagopyrum was five times as large as that of the solution of 

 baryta. These 15 grammes were then at least in the immediate 

 contact of 900 cubic centimetres of carbonic acid during the 

 day — i. e. 40 or 45 times more than that which might have escaped 

 reduction during exhalation. Besides, the exhalation by the 

 leaves is not really very great, unless the temperature in the 

 shade is 20° C"; at a lower temperature it generally decreases, 

 as does also the reduction, the opposite effects of which it seems 

 destined in part to correct. 



Now that the existence of two simultaneous and contrary pro- 

 cesses — namely, those of combustion and reduction — is no longer 

 doubtful, the notions regarding the respiration of plants hitherto 

 current must necessarily be considerably modified. Indeed it is 

 clear, that both in the day and in the night plants respire like 

 animals, but that this resjnration is during the day more or less 

 concealed by the contrary process : and it was for this reason 



