46 



HO-\V CUOrS FEED. 



air contained in plants, as well when the latter are remov- 

 ed from, as wlien they are subjected to, the action of light. 

 To collect the gas from the plants, the latter M'ere placed 

 in a glass vessel filled with water, from which all air had 

 been expelled by long boiling ami subsequent cooling in 

 full and tiglitly closed bottles. The vessel was then con- 

 nected with a simple apparatus in Avhich a vacuum was 

 produced by the fall of mercury, down a tube of 30 inches 

 height. The air contained within the cells of the plant 

 was thus drawn over into the vacuum and collected fot 

 examination. We give some of the results of the 6th 

 series of their examinations. " The Table shows the 

 Amount and Compositicm of the Gas evolve-l into a Tor- 

 ricellian vacuum by duplicate portions of oat-jilant, both 

 kept in the dark for some time, and then one exposed to 

 sunlight for about twenty minutes, when both were sub- 

 mitted to exhaustiou." 



] Per cent. 



Date, 



1858. 



July 31.1 



Aug. 2. 

 Aug. 2. 



These analyses show jilainly what it is that happens in 

 the cells of the plant. The atmosphei-ic air freely pene- 

 trates the vegetable tissues, (H. C. G., p. 288.) In dark- 

 ness, the oxygen that is thus contained within the plant 

 takes carbon from the vegetable matter and forms with it 

 carbonic acid. This process goes on witli comparative 

 rapidity, and the projiortion of oxygen may be diminish- 

 ed from 21, the normal percentage, to 4, or even, as in 

 some other experiments, to less than 1 per cent of the 

 volume of the air. Upon bringing the vegetable tissue 

 into sunlight, the carbonic acid previously formed within 

 the cells undergoes decomposition, with separation of its 



