OF CARBON. 51 



ides and earthy salts, for their perfection. Is 

 it to be expected, therefore, that when only one 

 of these necessaries is present, that a healthy 

 and vigorous plant is to be the result, or that 

 because such plants did not succeed, that the 

 element spoken of forms no part in the vege- 

 table economy? Certainly not, and the manner 

 in which these experiments were conducted is 

 opposed to all the rules of philosophical inquiry, 

 and to all the laws of modern chemistry. 



The other objection which has been taken 

 to the assimilation of carbon by plants has 

 arisen from the fact, that under certain circum- 

 stances plants give off carbonic acid gas instead 

 of assimilating it. In the chapter on the func- 

 tions of plants it has been explained that light 

 is an essential to the process of the assimilation 

 of carbon, and that the decomposition of carbo- 

 nic acid is arrested by darkness. But then, 

 namely at night, a true chemical action of the 

 oxygen of the atmosphere commences on the 

 leaves and other parts of the plant. This pro- 

 cess is not at all connected with the life of the 

 plant, as it acts in a similar way on the dead 

 plant; indeed, this result must not be consi- 

 dered in any way as the act of the plant itself, 

 but as the effect of the oxygen of the atmo- 

 sphere acting on the plant at a time when its 

 own powers of assimilation are in abeyance; 

 and yet, notwithstanding these adverse circum- 

 stances, it will be demonstrated still that plants 

 absorb more carbon during the day than is 

 given off by them during the night, and that in 

 regarding them as the great purifyers of the at- 



