b 



ON THE VEGETATION OF PLANTS. 159 



The green vegetable matter, which forms on all bodies, im* 

 mcrfed a confiderable time in water, might alfo have been one 

 of the fources of pure air, in fome of the experiments of Count 

 Rum ford. 



Secondly. Many philofophers fuppofe, that vegetables yield Plants donotde- 

 oxigenous gas by the decompofition of water. Its hidrogen f°™ P h ° e y d * a *" t ' 

 is faid to enter into plants, while its oxigen is fet at liberty in operate in pure 

 the form of pure air. water. 



If this opinion was true, oxigenous gas fhould be obtained 

 y expofing leaves in boiled, rain, diitilled, river, or lime 

 water, but this cannot be done. 



Thirdly. Some fuppofe that vegetables give oxigenous air to Plants do not 

 animals, and that the latter yield them azotic gas in return, ^ h a f g d ^ c ^- t 

 which they devour for food. oxigen and ab- 



If this hypothecs were juft, atmofpheric air would be in- forb azote > 

 creafed in purity by confining leaves in it when it contained 

 no fixed air; and its purity might alfo be increafed, after be- 

 ing previoufly diminished, by an additional quantity of azotic 

 air, in the fame manner. 



A handful of the leaves of euphorbia pida, nicotiana tobacco, for fefli leaves 

 t>uxus vulgaris, cinna glauca, mimofa julibrefcens, jaxus pro* do "°* a ? e<a at " 

 cumbens, coryllus avellana, Herculea fcetida, malva crifpa, 

 pinus ftrobus, colutea arborefcens, and epilobium, were fepa- 

 rately expofed four hours to the light of the fun, in forty ounce 

 meatures of atmofpheric air, and its purity was found to be 

 neither increafed nor diminifhed. After they had remained 

 fixteen hours in the air, no effect was produced on it. The 

 leaves were freth gathered, and no decay could be obferved 

 upon any part of them. 



When leaves are plucked promifcuoufiy, and are placed in though wounded 

 atmofpheric air either in the day or night, they diminilh its or decaying 

 .purity. Wherever a leaf is perforated, and this is very gene- C 

 rally done byinfech, let the perforation be ever fo fmall, the 

 part decays, and the coal of this decayed part uniting to the 

 oxigen of the atmofpheric air, generates carbonic acid, which 

 Jeflens its purity. 



The 



