gg FOOD OF THE VEGETATING PLANT. CHAP. II. 



vegetable food. But extract contains nitrogene; 

 for it yields by distillation a fluid impregnated with 

 ammonia. The difficulty, therefore, of accounting 

 for the introduction of nitrogene into the vegetating 

 plant, as well as for its existence in the mature 

 vegetable substance, is done away ; for although 

 the plant refuses it when presented in a gaseous 

 state, it is plain that it must admit it along with thtf 

 extract. 



But it seems also probable that a small quantity 

 of carbonic acid gas enters the plant along with the 

 extractive principle, as it is known to contain this 

 gas also. The mould analysed by Saussure was 

 quite dry before the commencement of the experi- 

 ment, and the water employed to moisten it con- 

 tained no carbonic acid. But the solution contained 

 some; for when it was mixed with lime-water, 

 carbonate of line was precipitated, though not in 

 a quantity much exceeding that of its precipitation 

 by spring-water in general. 100 cubic inches of 

 the solution yielded by experiment an air con- 

 taining two cubic inches of carbonic acid gas. This 

 is no doubt a small proportion : but it appears 

 from a variety of considerations, that the quantity 

 of this gas taken up by the roots of plants is not 

 great ; consequently they do not require a great sup- 

 from the soil. 



