234 
reason occurs why its hydrogen should not be libe- 
rated, as well as its oxygen is supposed to be ; for 
oxygen enters more abundantly into the composition 
of the vegetable than hydrogen docs, and may, 
therefore, be supposed to possess an affinity equally 
strong for the other elements of the vegetable sub- 
stance. Neither, if we admit the liberation of oxy- 
gen by these means, does it follow, that the mere 
absence of hydrogen is sufficient to authorise the 
conclusion that it has actually combined with the 
plant, and been converted into vegetable matter ; 
for, as far as observation yet goes, organised bodies 
do not appear to be increased in bulk, by matter sup- 
plied in an elementary form, but in a state of com- 
bination ; and the augmentation, which vegetables 
receive by the function of assimilation, seems to be 
very different from the mere aggregation of particles, 
which form an inanimate substance by the operation 
of chemical affinity, or by the laws of crystallization. 
518. The subject of the decomposition of water in 
vegetation has particularly engaged the attention of 
M. de Saussure. He observes that plants, vegetating, 
by the aid of distilled water, in oxygen gas, or in 
common air deprived of its carbonic acid, augment 
their weight. This increase of weight, however, af- 
fords, says he, no proof of the decomposition of the 
water, nor of the fixation of its elements, since it 
may be owing to the mere introduction of that fluid 
into the vegetable ; and, from many experiments, he 
satisfied himself, that, when plants are reduced to 
the same state of dryness before and after the experi- 
ment, this apparent augmentation of their weight is 
