OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
465 
celled, as no longer needed, the spores to which it was applied being recognized as 
those of Volkmannia Dawsoni. 
Calamites . 
Our knowledge of the structure of the cortical tissues of Calamites is yet very 
imperfect. A specimen from the Gannister bed at Moorside, near Ashton-under-Lyne, 
for which I am indebted to Mr. George Wild, supplies a new fact. In the memoir, 
Part IX., figs. 8-10 and 13, I have represented the primitive undifferentiated state 
of the cortical parenchyma of Calamites; and in figs. 14 and 15 of the same memoir, I 
have shown that a thick prosenchymatous layer was formed in the bark of some older 
stems. In Mr. Wild’s specimen, fig. 19, the vasculo-medullary axis presents the 
usual features, except that the vascular wedges are more detached than ordinary 
owing to the partial disappearance of the cells of the primary medullary rays. The 
innermost bark, a, differs but little from the primitive state seen in the figs. 8-10 and 
13 just referred to ; but at b we have a hypodermal zone of specialised bundles of 
what seem to have been prosen chymatous cells. Each bundle has a triangular section, 
the apex being centripetal, and is from '012 to '008 from base to apex. The outer¬ 
most bark, c, appears to have been a thin epidermal layer, some '003 to '002 in thickness. 
The peripheral border of this zone is sharply defined and entire, being wholly devoid 
of the crenulated contour so long supposed to have characterised the exteriors of sec¬ 
tions of the Calamites. Every definite fact hitherto discovered demonstrates that 
those outer surfaces possessed neither longitudinal flutings nor nodal constrictions. 
Whether the fibrous bundles just described are the beginnings of the prosen chymatous 
zone shown in figs. 14 and 15 of my ninth memoir, or whether they are peculiar to 
some special form of Calamite, cannot now be determined. The specimen described 
has a diameter of '25. 
Lepidodendroid plants. 
In several of my memoirs I have called attention to the gradual growth that took 
place in the diameter of the Lepidodendoid medulla owing to the multiplication of 
the medullary cells, and also to a contemporaneous increase that took place in the size 
of the surrounding non-exogenous vascular cylinder or “ etui medullaire” of Brong- 
niart, as well as in the number of its component vessels. Hitherto, however, 1 have 
failed to discover any example of natura naturans in either of these respects. But I 
found in a collection of sections submitted to me by Mr. Norman, of City Hoad, 
united Volkmannia with Asterophyllites, believing the former to be the fruiting branches of the latter. 
But the limits and distinctive characteristics of the genus Asterophyllites are themselves undefined, and, 
as yet, sub judice. Since I cannot identify my Volkmannia Dawsoni with any of the genera recognized 
by Schriper or by Professor Weiss, of Berlin, and I have not, as yet, obtained so accurate a knowledge 
of the orientation of the sporangiophores as would alone justify me in making it the type of a new genus, 
the strobilus may be left provisionally where I placed it in my previous memoir. 
