SECT. VI. ELABORATION OF OXYGENE. l6l 



they contained with the oxygene of their atmos- 

 phere ; the juice of the plant was coagulated. 

 Hence the oxygene inhaled by the leaf of the vege- 

 tating plant seems also to form carbonic acid gas 

 with the carbon which the leaf already contains ; 

 and in this state it probably remains in the paren- 

 chyma, till exposed to the action of light. There is 

 not indeed any direct proof that this is the fact ; but 

 there is no other supposition that will explain the 

 phenomena of the process so well. 



But if the oxygene inhaled by the plant is thus Affinityby 

 converted into carbonic acid, and condensed in the xygeneis 

 parenchyma, by what affinity is it retained? It retamed> 

 cannot be extricated by placing the plant in the 

 vacuum of an air pump. Six cubic inches of a 

 Cactus which had inhaled during one night four 

 cubic inches of oxygene, gave out in the vacuum 

 of an air pump only one cubic inch of air contain- 

 ing not more than T y^ of oxygene gas. A heat, 

 without light, sufficiently moderate not to destroy 

 the vegetable, produced no better effect. It is re- 

 tained therefore by an affinity too strong to be over- 

 come by such means. It is overcome, however, by 

 means of the action of the sun's light, as is demon- 

 strated by the clearest evidence ; but how the light 

 acts is not known. 



The property then which plants possess of in- 

 haling and evolving oxygene in the night and day 

 is analogous, and seems to be subordinate, to that by 

 which they decompose carbonic acid. The green 



VOL. II. M 



