22 BOTANICAL GAZETTE ~ [JANUARY 
continually thinner walled toward the medulla. These strands 
usually have an accompanying mucilage passage on the outer 
face, and are in constant (7) process of formation toward the 
center. Within this zone, vascular bundles, distinguished by 
their broad scalariform vessels, appear, and increase in number 
toward the central region. The central axis consists of a rather 
broad tract of parenchyma tissue, through which the vascular 
bundles are distributed in large numbers. 
From this point of view, and with due allowance for the 
effects of compression, it is possible to trace a striking similarity 
in several respects to a species of Myeloxylon described by 
Solms-Laubach,’ and more particularly in certain respects to 
specimens of Myelopteris described by Williamson. The evi- 
dence is both clear and direct that this plant must be considered 
as belonging to that peculiar group for which the name 
Myelopteris, proposed by Renault, has been most generally 
employed. 
In 1832, Cotta described certain fossils from the Carbonifer- 
ous of Europe under the name of Medullosa, which has more 
recently become merged in that of Myelopteris. Williamson, 
however, informs us that Cotta’s figures of MZ. elegans are wholly 
misleading, the structure being represented in a much exagger- 
ated form, while his two species, M. stellata and M. porosa, 
remain too obscure to be depended upon without further evi- 
dence than has come down to us.* The genus Medullosa, 
nevertheless, constitutes the basis of that group of plants 
which, passing under several names, has finally come to be known 
under that of Myelopteris. 
In 1845, Corda assigned to his genus Palmacites two plants — 
from the Coal Measures of Bohemia, under the names of P. 
carbonigenus and P. leptoxylon. An examination of Corda’s 
figures shows that there is no es great resemblance, although 
*2 Foss. Bot. 161, ke. 1gA. 
13 Foss. plants of the Coal Measures. Phil. Trans. 166: figs. 1, ae 
*4 Foss. plants of the Coal Measures. Phil. Trans. 166". 
: ican Geet ea oer 1845. 
