50 OF THE ASSIMILATION OF CARBON. 



Grischow to new investigations, by which they 

 ascertained, that under such conditions plants do 

 really absorb oxygen and emit carbonic acid ; but 

 that the whole volume of air undergoes diminution 

 at the same time. From the latter fact it follows, 

 that the quantity of oxygen gas absorbed is greater 

 than the volume of carbonic acid separated ; for, if 

 this were not the case, no diminution could occur. 

 These facts cannot be doubted, but the views based 

 on them have been so false, that nothing, except the 

 total want of observation and the utmost ignorance 

 of the chemical relations of plants to the atmo- 

 sphere, can account for their adoption. 



It is known that nitrogen, hydrogen, and a num- 

 ber of other gases, exercise a peculiar, and in gen- 

 eral an injurious influence upon living plants. Is it, 

 then, probable, that oxygen, one of the most ener- 

 getic agents in nature, should remain without influ- 

 ence on plants when one of their peculiar processes 

 of assimilation has ceased ? 



It is true that the decomposition of carbonic acid 

 is arrested by absence of light. But then, namely, 

 at night, a true chemical process commences, in 

 consequence of the action of the oxygen in the air, 

 upon the organic substances composing the leaves, 

 blossoms, and fruit. This process is not at all con- 

 nected with the life of the vegetable organism, 

 because it goes on in a dead plant exactly as in a 

 living one. 



The substances composing the leaves of different 

 plants being known, it is a matter of the greatest 

 ease and certainty to calculate which of them, dur- 

 ing life, should absorb most oxygen by chemical 

 action when the influence of light is withdrawn. 



The leaves and green parts of all plants contain- 

 ing volatile oils or volatile constituents in general, 

 which change into resin by the absorption of oxygen, 

 should absorb more than other parts which are free 

 from such substances. Those leaves, also, which 

 contain either the constituents of nut-galls, or com- 



