c 



inonst 



204 



fusion, are demonstrated by science, to be ministra- 

 tions of divine intelligence, and connected with the or- 

 der and harmony of our system. 



I have reasoned, in a former part of this Lecture, 

 against the close analogy which some persons have as- 

 sumed between the absorption of oxygene and the for- 

 mation of carbonic acid gas in germination, and in the 

 respiration of the foetus. Similar arguments will ap- 

 ply against the pursuit of this analogy between the 

 functions of the leaves of the adult plant, and those ot 

 the lungs of the adult animal. Plants grow vigorous- 

 ly only when supplied with light ; and most species 

 die if deprived of it. It cannot be supposed that the 

 production of oxygene from the leaf, which is known 

 to be connected with its natural colour, is the exertion 

 of a diseased function, or that it can acquire carbon in 

 the day-time, when it is in most vigorous growth, 

 when the sap is rising, when all its powers of obtain- 

 ing nourishment are exerted ; merely for the purpose 

 of giving it off again in the night, when its leaves are 

 closed, when the motion of the sap is imperfect, and 

 when it is in a state approaching to that of quiescence. 

 Many plants that grow upon rocks, or soils, contain- 

 ing no carbonic matter, can only be supposed to ac- 

 quire their charcoal from the carbonic acid gas in the 

 atmosphere ; and the leaf may be considered at the 

 same time as an organ of absorption, and an organ 

 in which the sap may undergo different chemical 

 changes. 



When pure water only is absorbed by the roots 

 of plants, the fluid, in passing into the leaves, will 



