54 THE STEM. 
an internal one, which is converted into alburnum. A new 
cambium exudes from the outer surface of the internal layer, 
and forms a new liber, which undergoes similar changes. 
“ Every year,” says Grew, “ the bark of a tree is di 
into two parts, and distributed two contrary ways : 
outer part falleth off towards the skin, and at length beee 
skin itself; the inmost portion of the bark is annually distri- 
buted and added to the wood.” This opinion is now a 
doned, and the theory now generally adopted is that of 
Thouars. 
175. Whatever may be the mode in which the form: 
of the new layers takes place, it is known that the new 1 
ter which forms them descends from the leaf, buds, 
leaves, either in the innermost layers of the bark, or be 
it and the alburnum. Pa 
176. If all the buds or leaves be removed from the 
part of a branch, no increase in diameter will take p 
above those that are left. If a ring of bark be remo 
a tree, the part below will not increase in thickness, 
upper lip of the wound will heal quickly, while the 
lip will not. This operation has been recommended 
ringgit ‘are must be fake o make te rng ery 
in order that the parts may easily reunite. S 
i Fe If a ligature be placed tightly round the bark 
tree, the part above the ligature will swell, but not the 
below ; Sc thnERNT pcr 
