46 HICK : SOME RECENT ADVANCES IN BRITISH PALEOBOTANY. 
nothing was known of their structure.* But no such necessity exists 
now. In working out the primary structure of the stem, my attention 
was frequently arrested by sections of leaves which, from certain 
well-marked histological characters, I concluded were the leaves of 
the Calamitean stems associated with them. Subsequently demon- 
strative proof of this conclusion was obtained from preparations made 
by Mr. Binns, of Halifax, and in April of this year a detailed des- 
cription of these leaves was communicated to the Manchester Literary 
and Philosophical Society.f So far as I can discover, this is the first 
and only account hitherto published of the structure of the leaves of 
Calamites, and this being so, a brief description of the chief features 
may not be unacceptable here, though full details must be sought in 
the paper referred to. 
Arranged in whorls at the nodes of the ultimate twigs, the leaves 
of the Arthropitys type of Calamites are small, linear structures, 
measuring approximatively 2\ millimetres (^^,5 inch) in length, 
I millimetre (7^3- inch) in breadth, and -^^ millimetre {-^q incli) in 
thickness. In transverse sections near the middle, the shape is not 
unlike that of the leaves of some Conifers, the upper surface being 
somewhat flattened, the lower more or less convex, and the margins 
extended into narrow blunt wings. At the outside of the section is 
an epidermis composed of a single layer of cells. Beneath this is a 
layer of palisade cells, continuous, or nearly so, all round the section, 
and forming a zone of assimilating tissue, which widens out at the 
side to form the obtuse wings. The central part of the leaf enclosed 
by the assimilating tissue is circular in section. Externally it carries 
a single layer of large cells, with black contents, forming a melas- 
matic " tissue, which is either continuous round the section or 
interrupted at the middle point of the upper side. Within the 
" melasmatic layer " we have a circular group of apparently cellular 
elements, in which is placed, excentrically and nearer the lower side, 
the transverse section of a very delicate vascular strand. 
Towards the base and apex of the leaf the transverse sections 
show a number of minor modifications in shape and structure, but in 
* Loc. cit., p. 5. 
t Mem. and Proc. of the Manch. Lit. and Phil. Soc. , series 4, vol. ix., 1894-5. 
