Chap. II.] 
COURSE OF THE SAP. 
79 
are for thinking so; the same, perhaps, as for 
thinking that all heart-wood is dead-wood. 
What other parts of the tree is the Doctor pre¬ 
pared to dispense with ? That a tree will live 
when the original central pith, and nearly all 
the heart-wood, are dead and gone , we know; 
and so will a man when one of his lungs is gone: 
and the man and the tree are equally benefited 
by the loss. 
The difference in size, between the top of the 
pith of one year’s shoot, and the base of the 
next, may also be seen in Plate I. p. 232. And 
in regard to the disappearance of the pith, even 
the layers of wood, which may be counted on 
this board, give thirty years of age to the lower 
pith, and twenty-nine to the upper one; but 
they are possibly much older, and perhaps half 
a century of pressure from without has neither 
exterminated them nor even reduced the lower 
end of the upper shoot to the same size as the 
upper end of the lower shoot. And I think it 
probable that each is of the exact shape and size 
that nature formed it the first year it grew. 
Again, you have only to examine a newly cut 
tree of any sort, and, if sound, you will see the 
pith, though around it you may count from 50 
to 150 years’ growth. In drying, after the trees 
