224 
Lindsey .— The Branching and Branch 
The Branch Theories of the Origin of the Scar. 
In 1907 D. M. S. Watson (12) described a specimen of Bothrodendron 
in the Manchester Museum, and explained that it showed the ulodendroid 
scar to be left by a dehiscent branch, the base of which occupied the whole 
area of the scar. 
The surface of the scar showed leaf-traces running out to the branch. 
M. Renier (7) in his monograph described a specimen in which a branch 
of Bothrodendron was seen on one side ‘ of a very thin plate of shale *, while 
in the same position, on the other 
side, was a ulodendroid scar with 
an eccentric umbilicus. He de¬ 
scribes this as indisputable evi¬ 
dence in favour of the branch 
theory. But, arguing from speci¬ 
mens of Lepidodendron , his con¬ 
clusions as to the way in which 
the branch was joined to the 
stem show that his conception of 
a branch theory differs funda¬ 
mentally from Watson’s. The one 
(Watson’s) supposes the branch 
to have been attached to the whole 
area of the scar, and to have 
been provided with some branch- 
shedding mechanism such as a 
layer of cork, and may therefore 
be described as the Abscission 
Layer Theory. 
The other (Renier’s) supposes 
the branch to have been attached 
to the stem by the umbilicus 
alone, that the branch ‘ had a 
conical base like the branch of 
a calamite ’, and that the rest of the scar was formed by pressure as the 
branch and trunk grew in size simultaneously. This may therefore be 
known as the Umbilical Attachment Theory. 
Text-figs. 1 and 2 show the essential differences between these two 
theories; in the case of the umbilical attachment theory the cortex of the 
branch was supposed to adhere to that of the stem over the area of the 
scar. Therefore the markings on the scar represent the markings on 
the inner side of the outer cortex of the branch, and bear no relationship 
with the leaf-traces of the stem. 
theory. c.b. y cortex of branch; c.s., cortex of stem; 
leaf-traces of stem are represented by dotted lines, 
leaf-traces of branch by continuous lines; the prin¬ 
cipal vascular axes are shaded. 
