Vlll 
CONTENTS. 
Page 
Where is the sap elaborated ? Whence the new growth 
in girthing deposited ? - - - 50 
Sap supposed to be elaborated in the leaf - - 51 
Growth in girthing supposed to be deposited from this 
elaborated sap in returning down the bark - - 51 
First office of the leaf, transpiration and excretion - 51 
Leaf supposed by some to absorb the food of plants - 53 
Second office of the leaf, the formation of winter-bud - 67 
Third office of the leaf, the changing of the sap from the 
upward conduit, the wood, to the downward conduit, 
the bark - - - - - - 68 
The growth in girthing is from the downward sap, or 
dependent on it; proof by experiment - - 68 
And supposed to be deposited from the bark — - 69 
But elaboration certainly takes place before the sap 
reaches the leaf - - - - - 71 
And also after it quits the leaf - - - 71 
Received theories of growth in girthing - - 72 
The pith or medulla, and medullary rays or silver grain 73 
Medullary rays longitudinal plates, only bounded in 
length by the height of trees and length of branches 
and roots - - - - - - 74 
The shake, and cup-shake - - - - 74 
Lateral as well as longitudinal flow of sap through the 
whole wood - - - - - 76 
The longitudinal pith-channels extend throughout the 
tree, from the pith of the original seedling to the 
finest ramifications of the roots and branches of the 
largest tree which is entirely alive - - - 77 
Diminution of the size of the pith and its disappearance 
vulgar errors - - - - - 78 
Whether the pith is the conduit of the upper sap or not 80 
Do the central piths of budded buds, of grafts, and of 
the shoots of coppice-wood, communicate with Du- 
trochet’s concentrical piths ? - - - 81 
Office of the pith unknown - - - - 85 
As the sap-channels are general, not peculiar, pruning 
increases the supply of the leader - - - 85 
