Researches on Vegetation. 3 1 1 



result of the combination of oxygen gas with the dead plant, 

 but that it is the residuum of the subtraction of the ele- 

 ments of the vegetable which have served to the production 

 of water and carbonic acid. 



It was of importance to compare the different vegetable 

 moulds \\ ith each other, and with the substances which had 

 not experienced destruction, to establish afterwards in what 

 manner thev might serve fur reproduction. 



Vegetable mould is an uniform substance, which seems 

 to differ only by a greater or less proportion of the soluble 

 part in water. 



It contains a greater proportion of carbon than the plants 

 from which it arises ; and we find here a consequence of 

 precedinf observations, which show that dead vegetables 

 acquire by their action on atmospheric air a greater propor- 

 tion of carbon, in consequence of the production of water 

 which takes place, than they lose by the formation of the 

 carbonic acid. 



The proportion of carl)on, however, in vegetable mould, 

 when it attains to a certain point of decomposition, does 

 not increase bv the continued action of the causes which 

 produce it : brought into contact with air, it continues to 

 form carbonic acid, and to produce water by the union of 

 the oxyoren and hydrogen it contains : but the latter pro- 

 duction is less considerable than before that epoch ; the 

 elements which are separated by this ulterior destruction 

 arc in proportions corresponding to those which form the 

 residuum, so that the vegetable mould continues to be de- 

 siroved without the residuum changing its nature. 



The vegetable mould retained all the principles which 

 arc found in the ashes of vegetables ; but these substances 

 resist the proofs to which they arc directly subjected : it is 

 only in the ashes resulting from their combustion that one 

 can distinguish them : moreover, a semi-vitrification may 

 prevent the potash from being dissolved by the water; it is 

 only by more energetic means that it can be separated. 



This series of researches has induced the author to deter- 

 mine the quantity of carbon furnished by a great number ot 

 vegetable substances : he took the most proper precautions 

 to obtain uniform carbon, and to fix the proportions: he 

 was obliged to neglect the part which is disengaged in a 

 gaseous combination ; but this disengagement ought not 

 to occasion any sensible difference between the comparative 

 <iuanliiies of tiic carbonaceous residuum. 



Having analysed the pha;nomena of vegetation which 



di-pend on the action of light, or the privation of it, in at- 



\j 4 mospheric 



