Lee. — The Morphology of Leaf-fall. 
79 
Gledxtschia triacanthos, Linn. 
The elucidation of the phenomena connected with the fall of the leaf 
in this species is rendered excessively difficult by the presence of various 
structural peculiarities of the leaf-base. As is well known, the latter organ 
in Gleditschia is much swollen, and hides a cavity which opens to the 
exterior by a transverse slit on the ventral surface, and in which repose the 
3~5 serially-arranged axillary buds (Text-fig. 14, a.b.s). Due to some 
factor — probably the assumption of the fixed light position — growth on one 
side of the leaf-base is almost 
invariably greater than on the 
other, with the result that 
this part is usually eccentric. 
Again, the stem-periderm 
(St. pd.) is rather deep seated 
and extends up to the narrow- 
est part of the leaf-base ; and 
the final complication arises 
from the fact that the quan- 
tity of sclerenchyma ( ScL ) 
accompanying the three vas- 
cular bundles which supply 
the leaf is large, and scarcely 
diminishes in any region. 
In addition to the scler- 
enchyma which surrounds the 
vascular ring of the stem, 
numerous groups of stone 
cells (St.) are present in the 
cortex, while the parenchy- 
matous cells of the latter 
often contain simple and com- 
pound crystals of calcium 
oxalate as well as varying 
quantities of starch. 
In the diagram (Text-fig. 14) a median longitudinal section of the 
leaf-base is shown. There is in this case no conspicuous massing of the 
protoplasm in the cells at the junction of cortex and petiole. The first 
indication of the approaching leaf-fall is given by the extension of a branch 
of the stem periderm in the direction of the vascular bundle, which is 
interrupted at the phloem of the leaf-trace by the sheath of sclerenchyma 
(P. pd.). A similar branch on the opposite side ends in contact with the 
xylem, and all the cells thus produced become only very feebly suberized. 
Text-fig. 14. Gleditschia triacanthos. Longitudinal 
section of leaf-base at time of leaf-fall. 
