On the Structure and Origin of the Ulodendroid Scar. 
BY 
D. M. S. WATSON, M.Sc., 
Lecturer on Vertebrate Palaeontology in University College , London. 
With Plate XXXVIII and two Figures in the Text. 
INCE my first discussion of the problem of the origin of the ulodendroid 
scar was published , 1 the description by M. A. Renier of a beautiful 
specimen, showing a branch still connected with a scar, has placed my 
primary conclusion beyond dispute . 2 M. Renier, however, believes that this 
branch was only attached to the umbilicus instead of the whole area of the 
scar, a view which seems to me to be negatived by all we know of the 
structure of lepidodendroid stems and to be inconsistent with the actual 
structure of well-preserved specimens of Ulodendron. 
The only other work of importance which has appeared since is the 
description by M. P. Bertrand of a Ulodendron with horizontally widened 
scars, each with a double umbilicus . 3 
M. Renier’s theory of the origin of ulodendroid scars is as follows : 
In the young condition a small branch issues laterally from the trunk, in the 
way which is perfectly familiar in structural as well as in impression material. 
Subsequently, by the secondary growth of both branch and trunk, the base 
of the former is included in the latter and swells rapidly, so as to acquire 
a conical form, where it is included in the cortex of the trunk. The real 
external surface of a ulodendroid scar on this theory is the inner aspect of 
the outer cortex of the conical base of the branch. 
Text-fig. i will, I hope, tend to make this view clearer. 
The evidence advanced in support of this theory is of two kinds — first, 
that drawn from impression material examined by its author, and second, 
supposed evidence drawn from published descriptions of petrified material : 
this latter appears to me to be evidence founded on misconceptions which 
could never have arisen had the author examined the original or other 
suitable structural material of Lepidodendrons with branches issuing 
laterally. 
1 Manchester Memoirs, lii, No. 4, 14 pp., 2 plates. 
2 Mdm. Soc. Geol. Belgique, t. ii, pp. 37-82, PI. VII-IX. 
3 Ann. de la Soc. Geol. du Nord, t. xxxix, 1910, pp. 345-61. 
[Annals of Botany, Vol. XXVIII. No. CXI. July, 1914.] 
