ON THE VEGETATION OF PLANTS. \Q\ 



plants, and to the temperature to which they are fubjecled, it 



appears more rational to afcribe the generation of it to the coal 



of the decayed parts uniting with the oxigen of the air in which 



they are placed. 



To determine whether plants would abforb or devour azotic Leaves cxpofed 



gas, eight ounce meafures of this air were mixed with thh-ty-mix'ture'of a"* 



two ounce meafures of atmofpheric air, fo that its purity wasmofpheric air 



reduced from 100 to 9 1 . A handful of the leaves of euphorbia * nd * zotc > P™" 

 •o i ii r • duced no cftett. 



pitta and coryllus avellana were feparately confined in forty 



ounce meafures of this air, and expofed to the influence of a 

 bright folar light rive hours. No carbonic acid gas was gener- 

 ated, and the purity of the air was exactly the fame as when 

 firft tried. No decayed portion could be obferved upon thefe 

 leaves. 



As it is acknowledged that the leaves, items, and roots of Leaves do not 



plants, feparate the oxigen from carbonic acid, it may be faid, ? m ?l the , at - 

 , , , . r r , \ mofphere by de- 



that the oxigenous portion of atmolphenc air is fupplied by the compofing its 



decompofition of this gas, as it is always found in the atmo- carbon)C S as > 



fphere, and often in water in which vegetables grow. quantity of this 



The quantity of carbonic acid gas in atmofpheric air, is g as is verv mi - 

 reckoned to be about one part in an hundred. It mult, how- nU e ' 

 ever, vary in different places. We would expect to find the 

 moft of it in cities, where it is formed by combuftion, refpira- 

 tion, fermentation, and putrefaction. If one meafure of the 

 air of any large city is thrown up over lime water in an eudio- 

 meter, no milky appearance will be produced, fo that the quan- 

 tity of carbonic acid in this air muit be extremely fmall. As 

 this gas is alfo feized upon by alkalis, earths, and metals, and 

 abforbed by water, the quantity floating in the atmofphere may 

 be lefs than one part in ten thoufand. 



When we confider likewife, that the oxigen is never fepa- an d plants dete- 

 rated from the carbonic acid by leaves, but when they are ex- « orate *• a ' ir 

 pofed, in contaa with it, to the light of the fun ; and that every mUCh m ° re# 

 perforation made in a living leaf, however minute, by an in- 

 fect, caufes the part to decay, and abforb oxigen by day and 

 by night ; and that, in the autumn in fome countries, all leaves 

 fall on the ground, ferment or putrify, and thus diminifh the 

 purity of common air ; and that the petals and fruit of vege- 

 tables have the fame effect, we muft pronounce, that the oxi- 

 genous portion of atmofpheric air cannot be fupplied by vege- 

 tation. 



Vol.11 — July, 1802. M Dr. 



