CHEMICAL CHANGES ACCOMPANYING ABSCISSION 
IN COLEUS BLUMEI 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 240 
HomeER C. SAMPSON 
Introduction 
Von Monat (13) in 1860 was the first to announce that previous 
to the fall of the leaf there is formed near the base of the petiole a 
definite separation layer in which abscission always occurs by the 
separation of the cells from each other with their walls still intact. 
The xylem tubes not being included in this separation layer are 
finally ruptured mechanically, and the leaf falls. He also called 
attention to the fact that abscission and the formation of a pro- 
tective tissue are two very distinct processes, and that the latter 
process might either precede or follow the former. WHESNER (17) 
in 1871 confirmed the observation of voN MOH in the main, and 
formulated the theory that the dissolution of the intercellular sub- 
stance of the cells of the separation layer is caused by the action of 
organic acids developed in the leaves. In 1886 Motiscu (14) 
suggested that a gum ferment might be the cause of this dissolution 
process. Two years later MANGIN (11), upon his discovery of the 
pectic nature of the middle lamella of cell walls in plants, indirectly 
advanced the knowledge of abscission. Since this discovery the 
abscission process has generally been referred to as a dissolution 
of the pectose and calcium pectate of the middle lamella. LLoypD 
(8, 9), assuming the organic acid theory of WIESNER, speaks of the 
process as a hydrolysis of these pectic compounds, and later (11) 
of cellulose also. 
The anatomical workers disagree somewhat on the amount of 
the cell wall altered during abscission. Lrxr (7) in 1911 reported 
the disappearance of the middle lamella only, and two years later 
Hannic (6) reported the same condition in the abscission of flowers, 
with the exception of a species of Mirabilis and of Oxybaphus, in 
which the entire cell wall disappeared. On the other hand, T1son 
Botanical Gazette, vol. 66] [32 
