NEGLECT OF CHEMISTRY BY BOTANISTS. 55 



tinually, during the day, from the points of the leaves 

 and twigs. These bubbles are seen most distinctly 

 when the rays of the sun fall upon the ice ; they are 

 very small at first, but collect under the ice and form 

 larger bubbles. They consist of pure oxygen gas. 

 Neither during the night, nor during the day when 

 the sun does not shine, are they observed to diminish 

 in quantity. The source of this oxygen is the car- 

 bonic acid dissolved in the water, which is absorbed 

 by the plants, but is again supplied to the water, by 

 the decay of vegetable substances contained in the 

 soil. If these plants absorb oxygen during the night, 

 it can be in no greater quantity than that which the 

 surrounding water holds in solution, for the gas, 

 which has been exhaled, is not again absorbed. The 

 action of water-plants cannot be supposed to form 

 an exception to a great law of nature, and the less 

 so, as the different action of aerial plants upon the 

 atmosphere is very easily explained. 



The opinion is not new, that the carbonic acid of 

 the air serves for the nutriment of plants, and that 

 its carbon is assimilated by them ; it has been ad- 

 mitted, defended, and argued for, by the soundest 

 and most intelligent natural philosophers, namely, by 

 Priestley, Sennebier, De Saussure, and even by In- 

 genhouss himself. There scarcely exists a theory 

 in natural science, in favor of which there are more 

 clear and decisive arguments. How, then, are we 

 to account for its not being received in its full extent 

 by most other physiologists, for its being even dis- 

 puted by many, and considered by a few as quite 

 refuted ? 



All this is due to two causes, which we shall now 

 consider. 



One is, that in botany the talent and labor of in- 

 quirers has been wholly spent in the examination of 

 form and structure : chemistry and physics have not 

 been allowed to sit in council upon the explanation 

 of the most simple processes ; their experience and 

 their laws have not been employed, though the most 



