ON THE FALL OF BRANCHLETS IN THE ASPEN (POPULUS TREMULA). 807 
myself to the Aspen, but in the oak and willow the changes are of 
a similar kind. In the larger branches of the Aspen the process 
does not occur, but branchlets half an inch i in diameter and below 
this readily allow of this aches! separation from their parent 
branch. Externally, the union of the bra nehlet with the branch 
offers to view a marked eulargotient; comparable with that which 
is seen at the base of the petioles in exogenous trees or at the 
bases of other deciduous stalks. The swelling or enlargement is 
concentric with the branchlet; and it is through the middle of this 
that the disarticulation takes place, and where the secret of the 
process lies. A longitudinal section of the enlargement shows a 
eneral increase in the sectional area of the medulla, the wood, and 
8 
inch in breadth; it crosses the bark at right angles to the surface 
of the enlargement, but the wood with slight obliquity wientils the 
parental branch, the zone elie as a era concave outwardly, or 
forming a very obtuse outward angle. et am bark be stripped off, 
the surface of the enlargement will be seen to present a series of 
longitudinal clefts, ibe woody iamnatetar sine disparted b 
intrusion of parenchyma. It is not that the woody tissue of the 
tree is peculiar, from any great natural and general shortness of 
the woody cells, or otherwise. Nor is it, again, that the death of 
he wood is itself the source of the separation. For if it be the 
however, a stump devoid of buds, the part dies, and is cleanly 
separated across its base, in the same way as the petiole of a 
deciduous leaf is cast off if the lamina be artificially removed. 
In the process of separation the branchlet is detached long before 
it presents the later signs of death; indeed it is difficult to believe 
sometimes that the fallen part has entered upon a total death ; fe = 
leaves and buds —. be still fresh spn a and its = not 
tinguishable by the eye from what i uivocally alive. The 
enlarged base of ake ; recently fallen branches dleplaye a soft 
pale yellow minutely granular surface, moist, an niformly convex, 
except at the margin, which, with the fissured sda of the cork, is 
slightly raised. After the detached parts have become dry, the 
wood presents, instead of a continuous surface, a series of deep 
Ww 
parent branch the corresponding surface acquires characters of a 
more permanent kind, and the resulting cicatrix is cupped, radi 
ridged in the situation of the wood and in a finer manner beyond, 
