104 
slowly, little or no air issued *. Unless, therefore, 
\ve suppose some cause capable of emptying the ves- 
sels of plants, it is difficult to conceive how the air 
can, simply by the force of mechanical pressure, en- 
ter and be transmitted through them. 
S45. All the circumstances, which have been al- 
ready stated, seem to shew that the air, which enters 
plants in an elastic form, is chiefly, if not entirely, 
diffused through their cellular structure, and does 
not gain admission into their vascular system. 
Hence the hollow stems of herbaceous plants, and 
the cellular structure of thick leaves, chiefly furnish 
air ; and when, therefore, the texture of these parts 
is broken down, the vegetable substance no longer 
exhibits the property of diminishing or attracting air. 
The universal distribution of this cellular tissue 
through the vegetable body, its loose and porous 
structure, its comparative emptiness, and the ready 
communication that probably obtains through its 
whole extent, fit it, in an especial manner, for re- 
ceiving and containing elastic fluids ; while the closer 
texture of the vascular system, its less general com- 
munication, and, above all, its occupancy by the ve- 
getable fluids, present, on every side, obstacles to 
the transmission of air. 
346. But granting that the air, which enters in an 
elastic form, resides chiefly in the cellular or paren- 
chymatous structure of plants, we have yet to inves- 
tigate the cause of its entrance, and the still more 
unaccountable fact of its existing in the vegetable, in 
* Veg. Statics, vol. i. 155. i 
