ioo Lee. — -The Morphology of Leaf-fall. 
(from a number of different points) occur in quick succession. The Pro- 
tective-layer (Text-fig. 19, L. P.) has a peculiar shape, curving upwards 
from all sides to meet the dorsal leaf-trace, and thus forming a prominent 
peg which projects above the general surface of the scar (Text-fig. 20, pr.). 
About this time tyloses and gummy lignin become apparent in the vessels 
of the vascular bundle near the leaf-base. 
The Separation-layer (S.L.), produced by slight division of the cells 
adjacent to the Protective-layer, possesses the usual characteristics, and 
separates in the ordinary way by disappearance of the middle lamellae of 
the outer cells. No Lignified-layer could be detected, but the remains of 
the Separation-layer form a slight ‘ parenchyme sacrifie 
It is usually not until the second season that divisions in the cells 
beneath the Protective-layer give rise to a cork cambium. In any case the 
layer of cork produced by the end of that season is never very extensive. 
Liriodendron tulipifera, Linn. 
Here the sequence of events is quite similar to that described for 
Catalpa , the only difference being the time of differentiation of the Pro- 
tective-layer. Numerous leaf-bases were examined, and it was found that 
in many little or no ligno-suberization had occurred previously to leaf-fall, 
all transitions being obtained at leaf-fail from the unchanged leaf-base to the 
one in which a completely ligno-suberized Protective-layer was present. 
In addition to this variation the presence of numerous mucilage cavities 
in the ground tissue must be noted. When these occur in the Protective- 
layer they undergo no division, though their walls usually become lignified. 
Magnolia sp. 
An unknown species of Magnolia was examined, and, so far as the 
observations went, was found to agree very closely with Liriodendron. 
General Discussion. 
Having now described the various species on which observations have 
been made, and arranged them under various types, it remains to examine 
the available evidence to see whether the scheme of classification advanced 
is vindicated, and at the same time, if possible, to draw one or two conclusions. 
The observations here recorded (on species examined by both of us) agree 
in the main with those of Tison, the variations — usually in time — probably 
being due to differences of climate and season. The essential modification 
in connexion with leaf-fall is the occurrence of the Separation-layer, which, 
therefore, was the first to appear in the course of evolution ; other modifica- 
tions connected with the improvement of the mechanism of the Separation- 
layer (i.e. the Lignified-layer) and with the protection of the underlying 
tissues (i. e. the Protective-layer) appeared later, the former in connexion 
