Lee . — The Morphology of Leaf -fall 89 
the Protective-layer are completely ligno-suberized at this time, in others 
the process is not completed until long after the leaf has fallen. 
Separation occurs in the usual way. The primary walls of the 
Separation-layer become slightly swollen, the middle lamellae become 
mucilaginous and disappear, leaving the neighbouring cells quite free. 
During the first winter divisions in the cells beneath the Protective- 
layer result in the formation of a cambium which gives rise to a continuous 
layer of cork. Later another cambium arises beneath the first one and 
traversing the vascular bundle adds greatly to the thickness of the layer of 
cork. 
Broussonetia papyrifera, Linn. 
Ficus Carica, Linn. 
These two plants are being taken together because in their leaf-fail 
phenomena, as well as in their general affinities, they are very similar. 
What slight differences there are will be pointed out in the course of 
the description. 
Starch granules and compound crystals of calcium oxalate have the 
usual distribution, while laticiferous tissue is abundant in both cortex 
and petiole. Periderm is present in the stem of Broussonetia previous 
to any change taking place in the leaf-base, though it is entirely absent 
from the stem of Ficus for some time after defoliation. Sclerenchyma 
is absent from stem and petiole in both species. 
The usual massing of the protoplasm in the cells of the leaf-base — 
which are also distinguished by the possession of starch granules and large 
nuclei — is followed by the production of new walls in the cells of this active 
area ; and although the first walls appear in the cells near the dorsal 
surface, the process spreads so rapidly that soon there is a complete layer 
of dividing cells, in each of which 1-4 new walls are produced. As 
these cells complete their divisions, their activity is transferred to the 
adjacent cells on the petiolar side, and in these the process of division 
is continued. The dividing cells always possess abundant protoplasm and 
starch granules ; and the sequence of events is continued until a layer 
4-8 cells in thickness have undergone division. The last layer to 
divide retains its protoplasm, and become the Separation-layer, this state- 
ment being especially true of Broussonetia ; in Ficus the Separation-layer 
may or may not have undergone division. All the new walls are approxi- 
mately parallel with each other and roughly at right angles to the axis 
of the petiole. 
Almost as soon as the first layer has completed its divisions, ligno- 
suberization commences and spreads in the direction of the Separation-layer. 
It is, however, very feeble, and its lower limit indefinite, and the chemical 
change accomplished before leaf-fall is very variable and usually not very 
