426 Dr. Gardner's Researches on the Functions of "Plants. 



3. Experiments were planned for the purpose of determi- 

 ning whether carbonic acid would penetrate into a vessel con- 

 taining common air through a barrier of vegetable epidermis, 

 and secondly, whether an inclosed mixture of gases of a theo- 

 retical composition would solicit the passage of both carbonic 

 acid and oxygen, and at the same time evolve nitrogen. 



4. A tube, five inches long and a third of an inch in bore, 

 with a flattened and ground end, was closed by a piece of 

 epidermis obtained from the leaf of the Madeira vine (Basella 

 lucida). The tube was then immersed in a mercurial trough 

 and filled to within an inch of the membrane ; on suspending 

 it by a wire it did not leak, though there was a pressure of 

 three inches of mercury. Clear lime-water was admitted to 

 displace the mercury, and the arrangement covered by a small 

 bell-jar containing atmospheric air with 10 per cent, carbonic 

 acid. In five hours the lime-water exhibited a distinct pel- 

 licle of carbonate of lime. The same result was obtained in 

 more or less time with the epidermis of the cabbage, Alanthus 

 alata, Chenopodium alburn^ and several species ofSedum. Some 

 specimens, as that from the balsam, leaked so fast as not to 

 sustain any mercurial column, whilst others maintained four 

 inches for thirty hours and more. 



5. A similar tube was closed with epidermis, and contained 

 an atmosphere of nitrogen 87, oxygen 13 per cent, over mer- 

 cury, and was covered with a bell-jar as above. The included 

 volume increased during nine hours from 400 to 433 mea- 

 sures, and on analysis consisted of N 76, O 17, 0O 2 7 per cent. 

 Hence the membrane comported itself as a simple porous 

 tissue, allowing nitrogen to pass out and admitting oxygen 

 and carbonic acid. This experiment was also repeated with 

 the foregoing specimens of epidermis, and no absolute varia- 

 tion perceived. 



II. The Constitution of the Internal Gas of Plants. 



6. The observations hitherto made on the included gases 

 of plants by Davy, Payen, Calvert and Ferrand, and others, 

 cannot be quoted here, because the disturbing effects of light 

 and other causes have not been sufficiently considered. It is 

 not merely the gas of a cavity which is required, but the com- 

 position of that which permeates the interior during the vigo- 

 rous state of the vegetable in sun-light. 



7. For the purpose of obtaining this, I transplanted in the 

 May of 184-5 a number of plants of Datura stramonium and of 

 "blue grass (Poa pratensis) into tumblers, and allowed them to 

 grow for several weeks before use. Having completed my 

 arrangements for analysing minutequantitiesof gas by asliding- 



