50 
COURSE OF THE SAP. 
[Part IT. 
Where is the 
sap elaborated ? 
Whence the new 
growth in 
girthing de¬ 
posited ? 
feet, I confess I do not see. But I guess that 
some day it will be seen, that turgescence acting 
on living organisation is the main mechanical 
power in the ascent of the sap. Cut a tree, 
indeed, or grub it if you please, and place it on 
its roots in a pond, and turgescence will by no 
means send the water up the dead wood. On 
the contrary, all but the immersed end of the 
tree, and its immediate neighbourhood, will dry 
as if it were in the timber-yard. This is as far 
as my horse Turgescence will carry me, which is 
not very far. And I end as I began—we are 
all in the dark about it! 
According to an experiment of Hales, which 
has been since verified by others, the sap rises 
with a force sufficient to support the pressure of 
a column of water of double the height which 
would burst an ordinary hogshead cask. And 
we see that it ascends to prodigious heights, yet 
we are ignorant how or by what agency. 
We see also the miraculous and universal sys¬ 
tem of transubstantiation with which we are 
surrounded in the vegetable world, yet we are 
not only ignorant of the chemistry which pro¬ 
duces this transubstantiation, — which, from 
absorbed moisture and gases, forms the immense 
variety and the immense quantity of all “ the 
