5Q FOOD OF THE VEGETATING PLANT. CHAP. I. 



SECTION II. 



Gases. 



WHEN it was found that water is insufficient to 

 constitute the sole food of plants, recourse was next 

 had to the assistance of the atmospheric air ; and 

 it was believed that the vital energy of the plant 

 is at least capable of furnishing all the different in- 

 gredients of the vegetable substance, by means of 

 decomposing and combining, in different ways, at- 

 mospheric air and water. But as this extravagant 

 conjecture is founded on no proof, it is conse- 

 quently of no value. It must be confessed, however, 

 Atmos- that atmospheric air is indispensably necessary to 

 nidTs 1C en ir *^ e health an ^ vigour of the plant, as may be seen 

 sable to ve- by looking at the different aspects of plants exposed 

 to a free circulation of air, and plants deprived of 

 it : the former are vigorous and luxuriant ; the 

 latter weak and stunted. It may be seen also by 

 means of experiment even upon a small scale. If 

 a plant is placed under a glass to which no new 

 supply of air has access, it soon begins to languish, 

 and at length withers and dies ; but particularly if 

 it is placed under the exhausted receiver of an air- 

 pump ; as might indeed be expected from the 

 failure of the germination of the seed in similar 

 circumstances. According to the experiments of 

 Saussure, plants of Peas, though completely deve- 

 loped and furnished with their leaves, died in the 



