Researches on Vegetation. 313 



Durino- the desiccation in the open air of plants which 

 have Hved without carbonic acid, there must be formed car- 

 bonic acid, according to the experiments of Saussure, an 

 abstract of which I have here presented, and water must be 

 produced at the same time ; since, instead of losing any of 

 their primitive weight, they make, on the contrary, a small 

 acquisition ; an increase of the vegetable substance, not 

 owing to a mere fixation of water, and which is greater 

 thanlhat announced by the balance, must have taken place 

 before the desiccation. 



When plants live in the light in atmospheric air, or in 

 any other gas deprived of carbonic acid, they give out a 

 little oxygen gas : according to Saussure, this oxygen gas is 

 thanked during each inspiration into carbonic acid, and is 

 agairT decomposed ; but the carbonic acid in its decomposi- 

 tion retains one-half of its oxygen : it thence follows that 

 in each expiration the proportion of the oxygen gas ought 

 to decrease, did not the decomposition of tlie water furnish 

 a supplement. 



It appears to me, then, that in common vegetation the 

 water and carbonic acid are decomi)Osed simultaneously by 

 the action of the light ; that tbe result of this decomposition 

 is, on the one hand, an emission of oxygen gas, which can- 

 not be ascribed to the one more than to the other; that, on 

 the other hand, there is formed a vegetable substance which 

 is inflammable, because it contains an excess of carbon and 

 hydrogen on account of the emission of the oxygen with 

 which they were saturated ; and that when a plant is de- 

 prived of carbonic acid it may still be supported, or make 

 some progress, by means of water alone. 



Having insulated the act of vegetation to discover its es- 

 sential conditions, and to deduce from them the principal 

 results, it was necessary to examine the circumstances of 

 conuiion vegetation to deicrmine its particular efiects, and 

 tbpecially to go back to the origin of the substances found 

 in plants, and which cannot be owing to oxygen, hydro- 

 gen, and the carbonic acid. 



This part of vegetable phvsiologv stood so much the 

 more in need of being explained, as (observations which ex- 

 hil)ited an imposinc; appearance of exactness had conducted 

 to buppo8iti(,-ns which could not be reconciled with phy.sical 

 theories. " Tull, Van lielmont, and even some modern 

 naturalists," savs Saussure, "■ ha\e endeavoured to show 

 that vegetables do not draw water from vegetable earth, and 

 that manure acts on the soil only by rurni>hing to plants a 



ni'iintcnnnc'! 



