Lee, — The Morphology of Leaf -fall, 93 
winter. The cork is at first small in amount, but the activity of the cam- 
bium in the second year produces a thick layer of periderm. 
Tyloses are usually very numerous and gummy lignin abundant. 
J. REGIA, Linn, and J. RUPESTRIS, Engelm. 
So far as these species have been examined, the sequence of events 
leading to and resulting from defoliation is very similar to what has been 
briefly described for J, nigra. 
CORNUS SANGUINEA, Linn. 
There is nothing remarkable in the external morphology of the leaf- 
base and adjacent parts in this well-known species. Each leaf — the junction 
of which with the stem is marked 
externally by a slight furrow — is 
supplied with three vascular bundles, 
which from the base of the petiole 
upwards are entirely free from scleren- 
chyma. Starch granules and com- 
pound crystals of calcium oxalate 
are present in the stem until very 
late in the first year. 
Some time previous to leaf-fall, a 
large area of cells (Z.P., Text-fig. 16) 
extending an appreciable distance up 
the petiole become distinguished by 
their greatly increased living and 
starchy contents, and begin to divide 
by walls which appear usually singly 
in each cell. The new walls, which 
are orientated in all directions, thicken 
slightly, and the whole area begins to 
undergo lignification. The latter process is usually very diffuse, and 
appears first in the upper part of the Protective-layer, from whence it 
spreads rapidly downwards until the whole of the cell-walls become more 
or less completely lignified. At the same time there is also a slight degree 
of suberization, which finally results in the production of an inner film of 
suberin on each cell-wall. The whole process is not complete until after 
leaf-fall, varying in this respect to a remarkable degree in the different 
examples, the progress made in each case being marked by the amount of 
protoplasm remaining in the cells. 
Divisions which lead to the formation of the Separation-layer take place 
at any early stage — almost as soon as any marked change has occurred 
in the cells destined to form the Protective-layer — and affect 2-3 rows 
Text-fig. 16. Cornus sanguined. Longitudinal 
section of leaf-base at time of leaf-fall. 
