312 Researches on Vegetation. 



mospheric air, the author examines those it exhibits when 

 green plants are placed in azotic gas, hydrogen gas, and 

 in vacuo. 



Plants provided with their green parts seem to be those 

 only which can vegetate in mediums deprived of oxygen 

 gas, because they diffuse through them this gas. When it 

 is taken from thi;m, in proportion as they produce it their 

 development is checked ; they absorb neither azotic nor hy- 

 drogen gas ; they vegetate in vaci/o as in azotic gas, pro- 

 vided the experiment is made under shelter from the direct 

 action of the sun's rays. Plants show a great dilfereuce in 

 these phagnomena according to their epochs. 



The author then proceeds to examine a vcrv important 

 question in vegetable physiology, that of the lixation and 

 decomposition of water. 



He shows that plants appropriate to themselves the oxy- 

 gen and hydrogen of water by making it lose the liquid 

 state; but this assimilation, he says, is not very striking, 

 except when they become incorporated at the same time 

 with carbon. 



To establish this assertion he placed plants in water, leav- 

 ing no carbonic acid in their atmosphere; they acquired a 

 very considerable weight, but they lost nearly the whole of 

 what they had acquired by desiccation in the open air : on 

 the other hand, when the vegetation was assisted by tiie 

 decomposition of the carbonic acid, the weight which they 

 retained after desiccation far surpassed that which might 

 have arisen from the carbon abandoned by the carbonic 

 acid. 



From this observation he concludes that all the oxygen 

 gas dispersed throughout the insulated atmosphere when the 

 green plants are exposed to the light, arises from the decom- 

 . position of the carbonic acid. 



I shall venture also to defend an opinion which differs 

 very little from that of Saussure and Sepebier, and which 

 appears to me to throw more light on the phaenomena of 

 vegetation. 



The immediate effect of light is the production of the 

 green juice of the leaves, which then undergoes various 

 changes in the plant ; but the green part arises from a re- 

 sinous substance, as has been shown by Piouellc : it cannot 

 be doujited that a resinous substance contains hvdrogcn 

 which is not in a state of saturation. The water, then, 

 must be decomposed in a plant which is supplied with no 

 other aliment than the water in the insulated atmosplicric 

 air, if it acquires there a green colour. 



Durir.fr 



