22 NUTRITION OF VEGETABLES. 



«wing to char- f^^ Mr. Cliaptal ]ias shown, that dry charcoal, alone or mixed 

 >cith earths of little solubility, does not penetrate into the 

 vessels of vegetables. 

 P'lantsaonot To add to the proofs, that vegetables have no need of 

 from the Sxith. ^^'^^^'"g carbon from the earth, I might mention high trees, 

 loaded with fruit, tliat grow and thrive on rocks or old walls, 

 totally destitute of vegetable mould ; and those vast forests, 

 the soil of which is pure sand extending far beyond the 

 roots. 



Opinion that J have now to examine the opinion, tliat vegetables absorb 



they derive it , i /. n • ,» i • 



from the at- their carbon from the small quantity of carbonic acid con- 



niosphere. tained in the astmosphere. Sennebier first announced this 



decomposition ; and T. Saussure afterward endeavoured to 



prove, that this very small quantity would be sufficient for 



all the vegetables that exist. But though this philosopher 



was persuvded of the utility of carbonic acid in vegetation, 



. be satisfied himself, that plants could grow in an atmospliere 



freed from it ; and he ascribed this grovvtii to the carbonic 



acid produced by the plants themselves, which they decom- 



^erimem^ *^^ posed after having formed it*. To prove this he exposed to 



the sun closed receivers, in which plants were growing, and 



suspended quicklime to the upper part of them. The plants 



soon grew yellow, and at the expiration of five days gave no 



signs of vegetation ; whence he inferred, that the absorption 



of carb<mic acid by the lime was the cause of their death, 



and that the elaboration of this acid was necessary to veget- 



The plants kil- ation in the sun. But I cannot be of his opinion. I have 



iK>urof the^*" examined the experiment careruUy, and satisfied myself, 



lime. that the death of the plants was not owing to the privation of 



carbonic acid alone, but to the lime itself in vapour. 



The following experiments convinced me of the volatility 

 of lime. 

 Jiine is in some ^' i^^^per tinged by repeated immersion in infusion of lit- 

 . measure yola- uiu$, then reddened, and afterward washed in water to re- 

 move its excess of acid, was suspended in a stopped phiul. 



* It is obvious, that the carbonic acid formed byAhe plants could not 

 furnish them with more of its base than it luid jjreviously taken from 

 them. Tr. 



1 into 



