1918] SAM PSON—ABSCISSION 23 
(15) as early as 1900, working with numerous species studied later 
by LEE, stated that in general the secondary membranes of the cell 
wall also undergo alteration and disappear, leaving only the thin 
tertiary membrane lining the cell lumen. Ltioyp (9, 10) has 
recently found the same condition in the abscission of cotton bolls 
and also in Mirabilis, instead of the disappearance of the entire cell 
wall as reported by HANNiIG. It seems improbable that the presence 
of weak organic acids would be sufficient to account for this extreme 
alteration of the cellulose walls of these cells. Certain authors - 
have suggested that the catalytic effect of enzymes may be an 
important factor in abscission, but experimental evidence has been 
wanting. 
Aside from his organic acid theory, WIESNER (21) in 1905 
suggested increased turgor as a cause of abscission under conditions 
of forced leaf-fall. Frrrrnc (5) in 1911 accepts this view to account 
for the rapid abscission of petals when forced. The suggestion 
lacks experimental confirmation, and the work of Hannic (6) 
indicates less need for its assumption. 
The external factors capable of accelerating leaf-fall are 
extremely diversified. These have been summarized in the main by 
Lioyp (8). The more important are high and low light intensity, 
high and low water supply, high temperatures and frost, low con- 
centrations of anesthetics, toxic-concentrations of acids and salts, 
and wounding of the blade. On the other hand, low concentrations 
of oxygen and high concentrations of anesthetics retard leaf-fall, a 
state of rigor being produced by the latter. 
The internal changes affected by these various external factors 
have received very little critical study. The work discussed in the 
present paper was undertaken to determine some of the internal 
changes accompanying abscission of leaves in Coleus Blumei var. 
Golden Bedder. This plant was chosen for study partly on 
account of its ease of propagation, but mainly for its simplicity of 
analysis owing to the absence of protective tissue at the time of 
abscission. 
Anatomy 
In order to appreciate fully the chemical changes taking place 
in the abscission layer, it is necessary not only to compare the 
