86 ON VEGETABLE AND MINERAL BODIES. 



the presence of light, on which their perfection in properties 

 and color inevitably rests. 



It would seem that they acquire all that is necessary to their 

 growth and stability, under the influence of light in the day, 

 and many plants are known (as discovered by Linnaeus) to 

 close their leaves at nighty and open them again at morn, to 

 taste the genial warmth and invigorating action of the rising 

 sun. 



Plants have been taken from the open air, and placed in a 

 dark room, and having closed or folded their leaves, the apart- 

 ment has been suddenly illuminated with lamps, on which they 

 have again unfolded them ; thus evincing the influence of arti- 

 ficial terrestrial radiating matter, and proving its analogy to 

 that of the solar beams. 



The general color of plants and trees in the state in which 

 they vegetate is green, importing the presence of azote, car- 

 bon, and hydrogen in their composition ; when their leaves fall, 

 and that fermentation takes place, a dissipation of iheir juices 

 ensues, they turn yellow, arid often of a reddish-brown, from 

 the discharge of a portion of their carbon in carbonic acid gas, 

 the quantity sufficient to retain the green color no longer 

 exists, and they are yellow from a predominancy of azote, or 

 reddish-brown, in proportion to the acid qualities retained by 

 them, from the presence of oxygen. 



Plants, in their growth, absorb hydrogen and azote, and 

 reject oxygen, but when they are no longer possessed of vege- 

 tative life, they combine with oxygen in their state of disso- 

 lution, which renders tl^e air in forests, in that season, the less 

 adapted to animal respiration. 



In metallic oxides where oxygen is known to be in combina- 

 tion, the color they assume is not uniformly red, but approaches 

 that tint in proportion to the quantity combined and corre- 

 sponding with the nature and original color of the metal 

 itself. Thus the first oxide of iron is yellow, the second ap- 

 proaching deep orange, or reddish-brown the third apuce color. 



