Lee. — The Morphology of Leaf -fall. 99 
aided by the diffusion from the broken vessels of the abundant gummy lignin 
which often covers the exposed surface. 
Towards the end of the second season the cells adjacent to the 
Protective-layer divide up to form a cork cambium, which, becoming con- 
tinuous with the phellogen of the stem, produces a conspicuous layer of 
regular cork cells towards the scar, as well as a small amount of phellogen 
towards the cortex. 
Catalpa Kaempferi, Sieb. 
The whole sequence of events in this species is quite similar to what 
has already been described by Tison of C. bignonioides. The junction of the 
stout cylindrical petiole with the stem is marked externally by a dark brown 
ring, while internally, considerable difference in size exists between the 
Text-fig. 20. Catalpa Kaempferi. 
Text-fig. 19. Catalpa Kaempferi. Longitudinal Portion of stem showing leaf-scars with 
section of leaf-base just before leaf-fail. projecting-peg (pr.)+ 
parenchymatous cells of these organs. Starch grains are present in the 
cortex only, but simple (octahedra) and compound crystals of calcium 
oxalate are abundant throughout. A single group of bundles supplies the 
leaf, the stereome accompanying which disappears completely at the leaf- 
base. A superficial periderm is present in the stem before leaf-fall. 
Aggregation of protoplasm in the cells of the leaf-base, division by 
walls formed singly in each cell, and lignification followed by suberization 
