SECT. II. GASES. 59 



in its atmosphere. But when a bunch was placed 

 in the same circumstance, with the addition of a 

 quantity of lime, the atmosphere was contaminated, 

 and the Grapes did not ripen.* Oxygene therefore 

 is essential to the developement of the vegetating 

 plant. 



But how is this beneficial effect operated? IsHowef- 

 the oxygene actually inhaled into the body of 

 the plant and converted into a vegetable food ; or 

 is its operation merely external ? Oxygene is ac- 

 tually inhaled, at least under certain circumstances. 

 Saussure having suspended a plant of the Cactus 

 punt ia, after sun-set, in a receiver containing 

 forty-eight cubic inches of atmospheric air deprived 

 of its carbonic acid, but of which six cubic inches 

 were displaced by the leaves, found early next 

 morning, after making the necessary corrections 

 relative to change of temperature and pressure, 

 that the atmosphere of the plant had diminished in 

 volume four cubic inches. The remaining air when 

 examined contained but T ^V of oxygene, though 

 before the introduction of the Cactus it had con- 

 tained -iW f the same gas. It follows, therefore, 

 that the diminution of quantity had affected the 

 oxygene only. But the oxygene did not exist in 

 the atmosphere of the plant under any combination 

 whatever ; for the application of lime water gave 

 no indications of the presence of carbonic acid. 

 The oxygene of the atmosphere, therefore, must 

 * Sur la Veg. chap. iii. sect. ix. 



