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Lee — The Morphology of Leaf-fall. 
A phenomenon which has been touched on briefly in the separate 
descriptions is the retention through the winter of dead leaves which 
are cast off in the following spring. Examples of species which do this are 
far from rare. In some cases, e. g. species of Quercus , Carpinus BeUdus, &c., 
only a certain proportion of the leaves are retained through the winter, 
while in others, such as coppiced beech, the whole of the leaves remain on 
the tree until the following spring. 
Although it is impossible to resist the conclusion that this phenomenon 
depends in some way on the decreased vitality of the plant, no adequate 
explanation can at present be suggested, and a full discussion of the pheno- 
menon will be left for a future paper. 
It was at first thought that it might be found possible to show some 
connexion between the degree of evolution of the plant and the type 
of leaf-fall structure ; but no such relation has been traced. A cursory 
examination of the list of species described shows that the individual classes 
(especially I and II) comprise plants derived indiscriminately from all the 
families of Dicotyledons. One advantage of the system of classification 
here proposed is that all species of the same genus so far examined fall 
naturally into the same class, and in this respect it appears to present some 
advantage over the more elaborate system proposed by Tison, where 
different species of the same genus may have to be referred to quite separate 
groups. 
Summary. 
In Dicotyledons the essential modification at the leaf-base in connexion 
with leaf-fail is the formation of a Separation-layer which is produced from 
existing cells with or without division. 
The leaf separates from the stem by the disappearance of the middle 
lamellae of the cells of the Separation-layer and the subsequent rupture of 
the sieve tubes and vessels of the leaf-trace at that level. 
A Lignified-layer may or may not be present, but a Protective-layer is 
invariably produced either before or after leaf-fall. 
The mode of formation of the Protective-layer is (i) by ligno- 
suberization of the cells of the leaf-base with or without irregular division ; 
(2) by ligno-suberization of cells produced by the continued division of 
a regular cambium. 
The following species have been examined : — 
Class /. 
(a) Castanea sativa, Mill. 
Hibiscus syriacus, Linn . 
Quercus palustris, Mnench . 
Ligustrum vulgare, Linn. 
Celtis occidentalis, Linn. 
Pyrus floribunda, Nichols . 
Ceanothus Gloire-de-Versailles 
(Garden origin). 
