Chap. II.] 
C0U11SE OF THE SAP. 
69 
when such a branch is sawed in two, length¬ 
wise, each additional annual layer may be 
counted above the ring, but none below it. But 
if the growth in girthing were deposited from the 
upward sap, the parts of a branch below the 
ring would be more favourably situated for it 
than the parts above the ring; also, if notches 
are made up a stem, the new growth comes first 
on the highest, and descends in succession. 
From these facts it is believed that, after the 
sap has been elaborated in the leaf in its descent 
through the bark, it deposits the new growth 
in girthing. If, however, the sap is elaborated 
solely in the leaf, and if the growth in girthing 
is deposited solely from the descending sap in 
the bark, the growth in girthing of the plum- 
stock of a grafted peach-tree should be peach; 
but the stock remains still plum, its roots 
plum, its shoots plum, and its suckers plum. 
On the other hand, if the elaboration were wholly 
in the root or stem, and the new growth in 
girthing from the upward sap, the wood and 
leaves of the peach would become plum. But 
purple beech* and variegated sycamore grow 
* Purple beeches may be raised from seed. I have one 
which I planted out in 1837, and have them of all ages since 
that. 
f 3 
and supposed 
to be deposited 
from the bark. 
