106 
bonic acid, and the subsequent attraction of this acid 
by the vegetable substance may favour and promote 
its farther entrance : and such, probably, is the 
cause why oxygen is received in a quantity so much 
exceeding that of eyery other gas, except carbonic 
acid. But some other cause, beside chemical change, 
seems, in many cases, to operate in the production of 
these phenomena, else there appears no reason why 
the organic form of the plant should be so essential to 
their completion. Now, we know, that, besides be- 
ing chemically attracted, air adheres to the surface^ 
of all bodies ; and, therefore, the more extensive the 
surface may be, the more extensive will be the adhe- 
sion between, it and the air. To us it appears pro- 
bable, that some such operation is exerted by the 
extended cellular structure of plants ; and therefore 
it is, that this structure aids the operation in ques- 
tion. It may, indeed, be said, that the same circum- 
stance would enlarge the sphere of chemical action,, 
and, by thus more extensively causing the production 
of carbonic acid, and its subsequent attraction by the 
vegetable substance, give rise to the phenomenon in 
question. But whether the elasticity of the air be, 
in these examples, overcome by this mechanical 
operation of adhesion, or by the effect of chemical 
change, or by both conjointly, we are compelled to 
conclude that cellular or fleshy leaves possess the pro- 
perty of receiving and retaining a quantity of elastic 
fluid, which, at the ordinary pressure and temperature 
of the atmosphere, considerably exceeds their own 
bulk. 
348. This conjoined operation of mechanical and 
chemical causes, which we have supposed to prc- 
