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On the Leaves of Calamites (Calamocladus Section). 
By H. Hamsuaw Tuomas, M.A., Curator of the Botanical Museum, Cambridge. 
(Communicated by A. C. Seward, F.R.S. Received December 2, 1910,— 
Read February 2, 1911.) 
(Abstract. ) 
In spite of the great progress which has been made in the study of Coal 
Measure plants, the subject of leaf structure has been largely neglected. 
The author is investigating the structure of the leaves of the principal 
groups of Paleozoic plants with the view of determining their morphological 
and biological characters, and also of obtaining some knowledge of the 
conditions under which they grew. 
The specimens of Calamite leaves described in this paper have been found 
chiefly in slides in existing collections, and most of the material originally 
came from the Halifax Hard Bed of the Lower Coal Measures. 
Most of the leaves found, were very small, being only 1 to 3 mm. long and 
‘0°8 to 1 mm. broad. They are falcate in shape, and were borne on slender 
twigs in alternating whorls of four. The structure of these slender twigs 
differs somewhat from that of the young Calamitean stems already described 
by Williamson and others, but it may be compared in some features with 
the structure of the young stems of some modern Equisetums. 
The tissues of the small leaves show a concentric arrangement. In the 
centre there is a vascular bundle consisting of four or five small tracheides 
surrounded by thin-walled elongated cells, The bundle is surrounded by 
a zone of cells with dense black contents, termed by the late Thomas Hick 
the melasmatic tissue, which is probably comparable with the bundle-sheath 
of the leaves of modern plants. ‘The cells of the palisade-like assimilating 
tissue abut on this, and have large spaces between them. The epidermis is 
thinner on the coneave side of the leaf, and the stomata are confined to this 
face. They are characterised by transversely striated guard cells, similar to 
those seen In many species of modern Equisetums. The leafy twigs just 
described seem to be identical with the impression-species Calamocladus 
charaeformis (Sternb.). Their structure seems to indicate that they grew in 
a pendulous manner. Specimens have been obtained showing variations 
in structure from the normal type. 
Four other types of leaf have been discovered, differing in size and in 
arrangement of tissues. In all of these there is a very conspicuous strand 
of sclerenchymatous fibres running up the adaxial side of the leaf and 
