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Upon the Bespiration of Plants. * By Messrs Edwards and 

 Colin. 



In tlie interesting science of vegetable physiology few or 

 no facts are to be found more beautiful than those connected 

 with the respiration of plants. The same remark, however, 

 can by no means be made concerning the theory which com- 

 bines these facts, and undertakes to explain them. In fact, 

 we have always experienced the greatest difficulty in admit- 

 ting this theory, whether considered in relation to the respi- 

 ration of the seed or of the leaves : and, in truth, scarcely 

 any other phenomenon has been recognised in the respiration 

 of the seed than the disengagement of carbonic acid. This 

 is usually explained by the combination of the oxygen of the 

 air with the carbon of the seed. According to this view, 

 the seed is supposed to be affected only by the atmosphere ; 

 the influence of water in this vital act of plants is considered 

 either as absolutely nothing, or is limited to that of preparation 

 and promotion, and it is held in no way to contribute to the pro- 

 duction of the gas which is disengaged. Tliis, then, is the first 

 difficulty respecting this theory of germination which presents 

 itself; and those which occur in regard to the explanation of 

 the respiration of the leaves are still more serious. During 

 the night, it is said carbonic acid is disengaged, whilst during 

 the day it is absorbed, and oxygen appears under the direct 

 rays of the sun. Here, then, are the facts, and here the ex- 

 planation which is affi^rded : the absorbed carbonic acid must 

 be decomposed by the plant, which again must appropriate 

 the carbon, and disengage the oxygen. 



But this capability of decomposing carbonic acid is confer- 

 ring upon the plant a power which it is very difficult to ad- 

 mit ; and it is very seldom found in the mineral kingdom, 

 where the very great simplicity of the composition of bodies 

 increases their decomposing power, and where the much 

 greater number oi elements, scattered throughout the diffe- 

 rent compounds of this kingdom, renders it probable that we 



• Read to tlie Academy of Sciences, Nov. 1838. From Annales des 

 Sciences Naturelles, for December 1838. 



