DAUBENY ON THE HYDROGEN OF PLANTS. 263 



the leaves enclosed in the jar, which were about fifty in 

 number, was calculated at not more than 300 square inches, 

 and yet there must have been added to the air of the jar as 

 much as 26*0 cubic inches of oxygen, in consequence of 

 the action of this surface upon the carbonic acid introduced. 



''But there is reason to believe, that even under the cir- 

 cumstances above stated (which appear more favorable to 

 the due performance of the functions of life than those to 

 which Mr. Ellis's plants were subjected), the amount of 

 oxygen evolved was much smaller than it would have been 

 in the open air, for I have succeeded, by introducing sev- 

 eral plants into the same jar of air in pretty quick succes- 

 sion, in raising the amount of oxygen contained from twen- 

 ty-one to thirty-nine per cent., and probably had not even 

 then attained the limit to which the increase of this con- 

 stituent might have been brought. 



" How great then must be the effect of an entire tree in 

 the open air under favorable circumstances ! and we must 

 recollect that, cceteris 'paribus^ the circumstances will be 

 favorable to the exertion of the vital energies of the plant, 

 within certain limits at least, in proportion as animal respi- 

 ration and animal putrefaction furnish to it a supply of car- 

 bonic acid. 



*' These experiments were published in the Philosophical 

 Transactions for 1836, and have been noticed in Dr. Lind- 

 ley's popular Introduction to Botany ; neither am I aware 

 that the deductions which were drawn from them have any- 

 where been disputed." 



Source of the Hydrogen of Plants; from Daubeny^s Lectures, 



(See Chapter IV.) 



**It would seem, I think, from the late important re- 

 searches of M. Payen, that the decomposition of water 

 commences subsequently to that of carbonic acid, whether 

 it be, that the former process requires a greater develop- 

 ment and energy in the vegetable functions, or that it takes 

 place in organs of a different description and of later 

 growth. 



''M. Payen seems to have established, that under the 

 general term of ligneous fibre, or lignin, we have hitherto 

 confounded at least two distinct substances, namely, that 

 which constitutes the walls of the cells, and that which, by 

 being deposited afterwards on the surfaces of the latter, 



