Chai\ II.] 
COURSE OF THE SAP. 
71 
a fourth elaboration of those saps may take 
place, on their junction between the wood and 
the bark, for the deposit of the new growth in 
girthing there. I confess that this is terrible 
guess-work; but I choose and state the theory 
which appears to me to have the least guess¬ 
work. As I have said throughout, all is doubt 
and difficulty. We may at least acknowledge our 
ignorance in the affair. To be ignorant is bad 
enough; but to be ignorant of one’s own igno¬ 
rance is worse. If a man knows that he has lost 
his way, he will at least go carefully; he will be 
on the look-out, and be the more likely to find it. 
It is certain that great chemical changes, or 
elaboration of the sap, must take place in the 
root or stem before it reaches the leaf since sap 
of very different qualities is drawn from the 
stems of different trees. Witness the sugar 
from the maple and birch, the resin from the 
fir, &c., &c., which are found in the heart-wood; 
also, the alteration of the heart-wood in density, 
and the change of sap-wood into heart-wood, 
argue elaboration in the stem, and deposit from 
the upward sap. 
It is also certain that great chemical changes, 
or elaboration of the sap, must take place in the 
bark, or elsewhere, after it has left the leaf; since 
But elaboration 
certainly 
takes place be¬ 
fore the sap 
reaches the 
leaf, 
and also after 
it quits the leaf. 
