]g2 PROCESS OF NUTRITION. CHAP. III. 



parts which effect the decomposition of the latter 

 effect also the alternate inhalation and extrication of 

 the former ; which two operations seem to be the 

 cause, the one of the other. When a leaf is put 

 into the shade immediately after having been ex- 

 posed to the light of the sun, it contains no carbonic 

 acid gas, because that gas has been decomposed by 

 Overcome the light ; but the oxygene of the atmospheric air 

 b 7 l'6 ht > w hich now penetrates and traverses the leaves, is 

 seized in its passage by the carbon of the plant. 

 And hence carbonic acid gas is again formed, which 

 loses its elasticity by its union with the water of 

 vegetation ; and which undergoes also a compression 

 by means of the vegetable structure, bounded how- 

 ever by certain limits, since plants which absorb the 

 most do not absorb more than T V of their volume. 

 They are now therefore saturated, and evolve by con- 

 sequence carbonic acid gas ; but the action of the 

 oxygene is in both cases the same namely, that of 

 forming carbonic acid with the carbon of the plant. 

 But forms Before saturation the carbonic acid is condensed in 

 carbonic ^ e p| an t ; but after saturation it is evolved, because 

 the plant can contain no more. Hence it follows 

 also that leaves do not immediately assimilate the 

 oxygene of the atmosphere which they inhale during 

 the night, unless they then decompose part of the 

 carbonic acid which is thus formed, and of which 

 experiment affords no proof. There can be no con- 

 clusion drawn from the phenomena produced in the 

 dark, in atmospheres deprived of oxygene ; because 



