6 2 
Lee . — The Morphology of Leaf -fall. 
feature of special interest in this connexion is that cells corresponding to 
the ordinary phelloderm (PI. IV, Fig. 4, ph .) are also cut off towards the 
cortex, and this despite the fact that as yet the stem phellogen has not been 
produced. It is not, however, until the end of the second season that the 
periderm becomes continuous across the vascular bundle by division of the 
living cells of the latter, and about the same time it joins on to the recently 
formed periderm of the stem (Text-fig. 7, P. pd. 1 ). All the elements above 
the Protective-periderm have by this time undergone a complete chemical 
change which, as has been pointed out above, varies with their morphological 
nature. 
of scar vv 11&WJL nao tasi oil 5 
Protective-periderm of last year. 
In the old scars it is of interest to note that the successive cork layers 
are thrown off, leaving in each case a perfectly plane surface (Text-fig. 8). 
It will be noticed later that this is a common phenomenon and corresponds 
to the exfoliation of the successive cork layers in the stem ; and one can 
scarcely avoid the inference that the throwing off in spring of the dead leaf 
in such cases as Quercus is but the ultimate result of the process, the be- 
ginnings of which we see in Tilia. 
Class II (b). Betula verrucosa. 
The leaf-fall phenomena in Betula vermcosa are identical in most 
respects with those which occur in the Lime. There is, however, under 
ordinary conditions, a difference in the sequence of the chief events, for in 
