190 THE LATE DR. NEWELL ARBER: CRITICAL STUDIES 
the effects of crushing before or since preservation and by growth-changes 
which took place after the leaves were shed but before fossilisation. These 
questions are worthy of re-examination on a broad comparative basis not 
confined to a few species, and involving the study of a large suite of materials, 
I do not propose to enter into this complicated subject here, except 
in regard to a single point in connection with the leaf scar, which has a 
particular significance in the case of the species of Lepidodendra which are 
here particularly in question. According to my view, the leaf sear is that 
portion of the leaf base which marks the point of the actual union of the part 
of the leaf which was normally and naturally shed, when it had reached a 
particular stage in its development, with that part of the leaf which remained 
permanently attached to the shoot. 
The sole characters which can be made use of in discriminating species of 
Lepidodendroid stems relate to the size, shape, and general characteristics 
of the leaf base as a whole and that particular region of the leaf base which 
we term the leaf scar. In the majority of British and Westphalian species, as 
is well known, the leaf scar is a perfectly definite area, usually clearly marked 
and more or less rhomboidal or triangular in shape. On well-preserved 
examples of the outer surface of the leaf bases, the prints of the vascular 
trace and the parichnos can usually be clearly distinguished within the leaf 
scar. In some, but not all, species, subparichnoid prints may occur beneath 
the leaf scar. Species of Lepidodendron, however, vary among themselves 
as regards the exact size and shape of the leaf sear and its position on the 
leaf base. 
But the point which I wish to emphasize here is that, in at least one 
British species, the leaf sear is of an entirely different nature. Itis not a 
superficial area, but a mere slit, transverse, more or less curved, and exhibits 
no prints comparable to the leaf trace and parichnoid prints of the more 
typical leaf scars, 
It may be recalled that exactly the same phenomenon is met with in the 
Paleozoic genus Cordaites (12. pl. 27). Here, in perhaps the majority of 
cases, the leaf scar is very short, slit-like, and non-print-bearing. But other 
eases occur in which the leaf scar has a considerable height as well as breadth, 
and here the row of leaf-trace prints may be often seen. 
In the case of L. ophiurus, Brongn., and L. lycopodioides, Sternb., which 
seem to me to have been considerably confused, the form of the leaf sear is 
alone sufficient to distinguish the species. L. ophiurus has, as I hope to show 
here, a superficial well-marked triangular sear, whereas L. lycopodioides has 
a mere slit. I commence by a re-examination of the characters of these two 
species, since here clearly lies the root of the difficulty. 
Tt is a curious fact that, although both these species are such common 
plants in the Coal Measures of Britain and on the Continent, they have been 
comparatively rarely figured, 
