SECT. VII. DECOMPOSITION OF WATER. 181 



do not, however, by a similar exposure augment 

 the volume of oxygene when confined in an at- 

 mosphere of oxygene gas, or of common air deprived 

 of its carbonic acid, because the carbonic acid which 

 they now form is the result of the combination of 

 their carbon only with the oxygene that surrounds 

 them, and not the entire produce of their own sub- 

 stance : hence it is only in such atmospheres that 

 the experimenter can form any judgment concerning 

 the direct decomposition of water by the plant. 



Succulent plants form indeed an exception with 

 regard to the augmentation of the volume of oxygene 

 when vegetating in an atmosphere of common air 

 deprived of its carbonic acid, but afford no proof of 

 the direct decomposition of water. Into a receiver 

 containing 41- cubic inches of atmospheric air pre- 

 viously deprived of its carbonic acid, a leaf or articu- 

 lation of the Cactus Opuntia was introduced, so as 

 that part of it was immersed in a glass containing dis- 

 tilled water, which was to serve as its nourishment ; 

 at the end of 31 days, when the experiment was 

 stopped, the leaf was still sound and vigorous ; it had 

 even formed roots of an inch in length, and aug- 

 mented its atmosphere 34- cubic inches. The eudio- 

 meter indicated the presence of 25 parts in the 

 hundred of oxygene, and the application of lime 

 water showed that it contained no carbonic acid; 

 hence the leaf had extricated in the space of a 

 month 3i- times its volume of oxygene, which could 

 be attributed to no other cause but that of the 

 1 



