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watery particles have been considerably dissipated 
by the transpiring functions of the leaves, and the 
mucilaginous, inflammable, and astringent con- 
stituents, increased by the agency of heat, light, 
and air, the continued impulse upwards from the 
alburnum forces the remaining inspissated fluid 
into the cortical vessels, which receive no other 
supply. In these, from its weight, its natural 
tendency must be to descend ; and the rapidity of 
the descent must depend upon the general con- 
sumption of the fluids of the bark in the living 
processes of vegetation ; for there is every reason 
to believe, that no fluid passes into the soil through 
the roots ; and it is impossible to conceive a free 
lateral communication between the absorbent ves- 
sels of the alburnum in the roots, and the trans- 
porting or carrying vessels of the bark ; for if such 
a communication existed, there is no reason why 
the sap should not rise through the bark as well as 
through the alburnum ; for the same physical 
powers would then operate upon both. 
Some authors have supposed that the sap rises in 
the alburnum, and descends through the bark in 
consequence of a power similar to that which pro- 
duces the circulation of the blood in animals ; a 
force analogous to the muscular force in the sides 
of the vessels. 
This analogy has, however, in general, been too 
much insisted upon and too loosely stated ; there are 
undoubtedy resemblances more or less remote in 
every part of created nature; but the irritability 
of the muscular fibre in animals and the contracti- 
