The Morphology of Leaf-fall. 
BY 
E. LEE, A.R.C.Sc. 
Late Marshal Scholar in the Imperial College of Science and Technology , South Kensington ; 
Assistant Lecturer in Botany , Birkbeck College , London. 
With Plates IV-VI and twenty Figures in the Text. 
F ROM the time of von Mohl’s classical paper in i860 down to the 
present day, the problem of the physiological and anatomical causes 
leading to and arising from the natural amputation of the leaf has, with the 
exception of a short note by Parkin and a passing reference by Woodhead, 
been exclusively attacked by Continental workers. In the present paper the 
aspect of the question of the natural amputation of the leaf will be purely 
anatomical and will relate only to Dicotyledons, and in them exclusively 
to those species which annually cast off their leaves. A first paper such as 
this is almost necessarily incomplete, but it is hoped soon to extend the 
present work to include the examination of other classes of defoliating plants 
as well as other aspects of this interesting question. 
Before passing to a detailed description of the types studied a short 
summary of the history of the subject will be given, and as the present 
work is purely anatomical, only a history of observations bearing on that 
aspect of the subject will now be presented. 
As early as the middle of the eighteenth century the phenomenon 
of leaf-fall had already attracted the serious attention of observers, for 
in 1758 Du Hamel maintained that — 
(1) A layer of cells at the base of the petiole always remained her- 
baceous, and was therefore incapable of supporting the leaf during the 
winter ; and 
(2) After the leaf had ceased to grow in consequence of excessive 
transpiration, the stem continued to increase in thickness, and this resulted 
in a tension which ruptured the fibres which unite the leaf to the stem. 
Although combated by Mustel (1781), who showed that there is 
a plentiful supply of cell-sap in the leaf at the time of leaf-fall, the different 
points in Du Hamel’s theory obtained many supporters, among whom were 
Murray (1785), Link (1812), and Petit-Thouars (1815). In 1796, however, 
another view was brought forward by Vrolick, who believed that the imme- 
[ Annals of Botany, Vol. XXV. No. XCVII. January, 1911.] 
