Lee . — The Morphology of Leaf-fall. 95 
marked Lignified-layer, while below it a new periderm is afterwards pro- 
duced, of which a small proportion is phelloderm (Lig. and P. pd . *). 
Cornus Mas, Linn. 
In all the essential stages C. Mas is very similar to C. sanguinea. It 
was remarked in the description of the latter species that much variation 
exists in the degree of completeness attained by the ligno-suberization of 
the Protective-layer before leaf-fall. This is carried to its extreme in 
C. Mas, where at the time mentioned no ligno-suberization has occurred. 
The later modifications and ultimate result are the same as in C. sanguinea . 
Nyssa sylvatica, Marsh. 
Leaf-fail in this species is very similar to that of Cornus sanguinea , and 
calls for no special description. A small difference which may be noted is 
the complete absence of the Lignified-layer, a slight formation of which 
was remarked in C. sanguinea. 
Ailanthus glandulosa, Desf. 
The petiole of A. glandtdosa is very stout and cylindrical, and its 
swollen base is delimited from the stem by a well-marked furrow ; while in 
a slight hollow on the upper face rests the small axillary bud. Internally 
the cells of the petiole are distinguished from those of the cortex by the 
absence from the former of granules of starch, numerous crystal clusters of 
calcium oxalate occurring in both tissues. 
A continuous ring of sclerenchyma surrounds the vascular cylinder in 
the stem. Five bundles leave the ring to supply each leaf, and as they pass 
out at different levels the sclerenchyma accompanying them decreases and 
finally disappears just below the junction of petiole and cortex. In the 
leaf-base the bundles divide up and later form a continuous ring (with 
internal groups), which traverses the petiole and which is supplied with 
an increasing quantity of sclerenchyma situated outside the bast. 
In the stem a periderm which arises in the outer layer of the cortex is 
invariably present before leaf-fall, and in many cases extends well up the 
petiole. 
The Protective-layer is formed by the irregular division of the cells at 
the base of the petiole, and, compared with the size of the latter, is relatively 
thin. It appears very early, and curves slightly towards the cortex. After 
each cell has divided 1-3 times the cell-walls become ligno-suberized, and 
finally lose their contents. The process of ligno-suberization and its results 
are invariably complete before leaf-fail, the living elements of the leaf-trace 
being the last to undergo change. Numerous crystal cells are enclosed 
within the Protective-layer, and without undergoing division they become 
