1^38] 



FARMERS' REGISTER. 



631 



of which I have repealed with similar results. 

 'I'lie absorption ol" carbonic acid iras and the pro- 

 I'uction of oxyiren are performed by the leaf; and 

 leaves recently separated from the tree effect the 

 rhaniie, when confined in portions of air contain- 

 inu; carbonic acid; and absorb carbonic acid and 

 prodnce oxyiren, even when immersed in water 

 holiling carbonic acid in solniion. 



The carbonic acid is probably absorbed by the 

 fluids in the cells of the green or parenchymatous 

 part of the leaf; and it is from this part that oxy- 

 gen gas is produced during the presence of light. 

 JVI. Scnnebier found that the leaf, from which the 

 epidermis was stripped ofl', continued to produce 

 oxygen when place(l in water containing carbonic 

 acid L'as, and the <ilobules of air rose from the de- 

 nuded parench_vma; and it is shown both from the 

 experiments of Sennebier and VVoodhouse, that 

 the leaves most abundant in parenchymatous 

 parts produce most oxygen in water impregnated 

 whh carbonic acid. 



Some few plants* will vegetate in an artificial 

 atmosphere, consisting principally of carbonic 

 acid, and many will irrow for some time in air 

 containing from one-half to one-third; but they 

 are not so healthy as when supplied with smaller 

 quantises of this elastic substance. 



Plants exposed to light have been found to pro- 

 duce oxviren gas in an elastic medium and in wa- 

 ter containing no carbonic acid gas; but in quan- 

 tities much smaller than when carbonic acid gas 

 was present. 



In the dark, no oxygen eras is produced by 

 plants, whatever be the elastic medium to which 

 they are exposed; and no carbonic acid absorbed. 

 In most cases, on the contrary, oxygen gas, if it 

 he present, is absorbed, and carbonic acid gas is 

 produced. 



In the changes that take place in the composi- 

 tion of the orgnnized parts it is probable that sac- 

 charine compounds are principally formed during 

 the absence of light; gum, woody fibre, oils, and 

 resins, during; its presence ; and the evolution of 

 carbonic acid gas, or its formation durincr the 

 night, may be necessary to give greater solubility 

 to certain compounds in the plant. I once sus- 

 pected that all the carbonic acid gas, produced by 

 plants in the nitrht. or in shade, misht be owing 

 to the decay of some part of the leaf, or epider- 

 mis; but the recent experiments of Mr. D. Ellis 

 are opposed to this idea; and I found that a per- 

 fectly healthy plant of celery, placed in a given 

 portion of air for a few hours onl^v, occasioned a 

 production of carbonic acid gas, and an absorp- 

 tion of oxygen. 



Some persons have supposed that plants ex- 

 posed in the free atmosphere to the vicissitudes of 

 sunshine and shade, light and darkness, consume 

 more oxygen than they produce, and that Iheir 

 permanent asrency upon air is similar to that of 

 animals; and this opinion is espoused by the 

 writer on the subject I have just quoted, in his in- 

 genious researches on vegetation. But all experi- 

 ments brought forwards in favor of this idea, and 

 particularly his experiments, have been made un- 

 der circumstances unfavorable to accuracy of re- 

 sult. The plants have been confined and supplied 

 with food in an unnatural manner; and the influ- 



* I found the Arenaria tenuifolia to produce oxygen 

 in carbonic acid, which was nearly pure. 



encc of light upon them has been very much di- 

 minished by the nature of the media through 

 which it passed. Plants confined in limited por- 

 tions of atmospheric air soon liccome diseased; 

 their leaves decay, and by their decomposition 

 they rapidly destroy the oxygen of (he air. In 

 some of the early experiments of Dr. Priestley, 

 before he was acriuainted with the agency of light 

 upon leaves, air that had supported combustion 

 and respiration, was found purified by the growth 

 of plants when they vvere exposed in it lor suc- 

 cessive days and nights; and his experiments are 

 the more unexceptionable, as the plants, in many 

 of them, grew in their natural states; and shoots, 

 or branches fiom them, only were introduced 

 through water into the confined atmosphere. 



I have made some few researches on this sub- 

 ject, and I shall describe their results. On the 

 12th of July, 1800, I placed a turf four inches 

 square, clothed with grass, principally meadow 

 fox-tail, and Avhite clover, in a porcelain dish, 

 standing in a shallow tray filled with water; I then 

 covered it with ajar of flint glass, containing 380 

 cubical inches of common air in its natural state. 

 It was exposed in a garden, so as to be liable to 

 the same changes with respect to light as in the 

 common air. On the 20th of July the results 

 were examined. There was an increase of the 

 volume of the gas, amounting to fifteen cubical 

 inches; but the temperature had changed from 

 64° to 71° ; and the pressure of the atmosphere, 

 which on the 12th had been equal to the support 

 of .30.1 inches of mercury, was now equal to that 

 of 30.2. Some of the leaves of the white clover, 

 and of the fox-tail were yellow, and the whole 

 appearance of the grass less healthy than when 

 it was first introduced. A cubical inch of the 

 gas, agitated in lime-water, gave a slight turbid- 

 ness to the water; and the absorption was not 

 quite y|^ of its volume: 100 parts of the residual 

 gas exposed to a solution of green sulphate ol' 

 iron, impregnated with nitrous gas, a substance 

 which rapidly absorbs oxygen from air, occasion- 

 ed a diminution to 80 parts; 100 parts of the air 

 of the garden occasioned a diminution to 79 parts. 



If the results of this experiment be calculated 

 upon, it will appear that the air had been slightly 

 deteriorated by the action of the grasses. ° But 

 the weather was unusually cloudy during the pro- 

 gress of the experiment; the plants had not been 

 supplied in a natural manner with carbonic acid 

 gas; and the quantity formed during the night, 

 and by the action of the fiided leaves, must liave 

 been partly dissolved by the water; and that this 

 was actually the case, 1 proved by pouring lime- 

 water into the water, when an immediate precipi- 

 tation was occasioned. The increase of azote I 

 am inclined to attribute to common air disengaged 

 from the water. 



The following experiment I consider as con- 

 ducted under circumstances more analogous to 

 those existing in nature. A turf four inches 

 square, from an irrigated meadow, clothed with 

 common meadow grass, meadow (ox-tail grass, 

 and vernal meadow grass, was placed in a porce- 

 lain dish, which swam on the surfiice of water 

 impregnated with carbonic acid gas. A vessel of 

 thin flint glass, of the capacity of 230 cubical 

 inches, having a funnel furnished with a stop-cock 

 inserted in the top, was made to cover the grass; 

 and the apparatus was exposed in an open place; 



