242 Proceedings of the Royal Physical Society. 
more or less deformed by mutual pressure. In the Leioder- 
marian forms they possess no cushion, and are circular from 
the absence of all pressure. 
ftemarks.—Following Weiss and Sterzel in tracing the 
changes which take place in the external appearance of the 
bark of Sigillaria Brardii, Brongt., we may commence with 
those Leiodermarian forms which have been described as 
Sigillaria spinulosa, Germar, and Sigillaria denudata, Gopp., 
on which the leaf-scars are distinct, show no trace of a leaf- 
cushion, and whose bark is ornamented with the peculiar 
shagreen sculpturing already described. It is not necessary 
to consider at present whether these forms arise from a rapid 
growth of the stem in the young state, or by increase in 
girth of the trunk at a subsequent period.? 
The next stage is that in which there are indications of a 
leaf-cushion, and such forms are described as sub-Leioder- 
maria or sub-Clathraria. To these corresponds the Sigillaria 
vhomboidea, Brongt. Here, also, the bark is usually orna- 
mented with the shagreen sculpture. 
In the succeeding progressive form the leaf-scar is placed 
on the upper part of a distinct and more or less elevated 
subspathulate cushion, whose upper margin is convex, the 
lateral concave, and the lower margin truncate. The plant 
has now assumed the Clathrarian form, and the shagreen 
ornamentation of the bark becomes less frequent. Of this 
type is the Sigillaria Wettinensis, Weiss. 
In the last form, the distinct contiguous rhomboidal leaf- 
cushions are separated by well-defined dividing furrows. 
On the smaller branches the leaf-cushions are frequently 
transversely rhomboidal. The cushions are generally smooth 
and free from ornamentation. The Sigillaria Brardii, Brongt., 
corresponds with this condition of the plant. 
The sequence of change just described is well seen on the 
small stem from the railway cutting at Florence Colliery, 
Longton, Staffordshire, which is shown natural size on Plate 
VII, Fig. 1. Commencing, however, in the reverse order 
to that given while tracing the variations through which 
1 It should be remembered, however, that such Leiodermarian forms occur 
inserted between Clathrarian portions of the stem, 
