77 
Lee . — The Morphology of Leaf -fall. 
latter but present in the cortex, while single and cluster crystals of calcium 
oxalate appear in cells of both tissues and of the leaf-base. A rather deep- 
seated periderm is present in the stem (PI. V, Fig. io, st. pd). 
The Protective-layer (Z.P.), at first distinguished by reason of its 
abundant living and starchy contents, becomes distinctly ligno-suberized 
long before leaf-fall, the process commencing at localized points, from whence 
it spreads rapidly, soon extending into the vascular bundle. Near the 
upper and lower boundaries of the Protective-layer the lignin appears to 
predominate ; the walls of the crystal cells undergo lignification only. A few 
tyloses appear in the larger vessels during the process. 
The Separation- layer (S. L.) is formed by the slight division of 1-3 
rows of cells, which as usual are distinguished by possession of much 
protoplasm and a few starch granules. Separation is effected by the 
mucilaginization and disappearance of the middle lamellae between the 
outer layers. No lignification occurs above the Separation-layer. 
In the second year a cork cambium arises beneath the Protective-layer, 
and traversing the vascular bundle, becomes continuous with the stem 
periderm. As in Diospyrus , a thin layer of cork is the result. 
Forsythia Fortunei, Hort. (= F. suspensa, Vahl.). 
The case of F. suspensa has been fully dealt with by Tison, who founds 
a type on the species. To his general description there is little to add, and 
only a short summary of the course of events will be given. The petiole 
is short and spreading towards the base, enclosing in its axil the two 
unequal buds. Neither externally nor internally is there any clear distinction 
between the petiole and stem except in presence of starch in the cells of the 
latter. A single vascular bundle supplies each leaf, and in traversing 
the cortex it loses the whole of the lignified stereome which at first 
accompanied it. 
The slight massing of the protoplasm in the cells of the leaf-base is 
followed by the more or less complete ligno-suberization of the cell-walls, 
the latter process commencing in the upper portion, and gradually spreading 
across and downwards until a fairly thick wedge-shaped Protective- layer 
has been produced. No previous divisions have occurred in these cells, 
and at this time few or no tyloses have appeared in the vessels of the leaf- 
trace at this level, although the living elements of the bundle have begun 
to undergo ligno-suberization. 
About this time in the average leaf-base the cells below the Protective- 
layer begin to divide regularly and give rise to a cambium which, without 
traversing the vascular bundle, soon becomes continuous with the well- 
marked phellogen of the stem. A few layers of cork may be produced, the 
number varying with the example and very probably with the position on 
the branch. 
