of Lepidostrobus Brownii , Schpr . 333 
those zones of somewhat similar nature which may be distin- 
guished in the cortex of some living species of Lycopodium , 
or those above noted in other Lepidodendra . M. Hovelacque 
has also traced with great detail the progress of the leaf-trace 
from the central stele to the leaf-cushion, its structure, and rela- 
tions to the surrounding tissues, and his results are interesting 
for comparison with those to be described below. 
Notwithstanding that in certain cases, such as the specimens 
of Lepidodendron selaginoides thus described by M. Hovelacque, 
the tissues appear as a continuous sequence, the occurrence of 
large gaps in many specimens calls for further consideration, 
while a comparison with living plants of Lycopodium and 
Selaginella will be important for the elucidation of the results. 
The discontinuity which is common in vegetative stems of 
Lepidodendron comes out even more strongly in most speci- 
mens of the axis of Lepidostrobus ; in these the tissues are 
often badly preserved, especially the phloem and the middle 
cortex. A brilliant exception is, however, found in the large 
cone of Lepidostrobus Brownii in the British Museum, known 
there as Brown’s cone. This silicified fossil shows, in an 
unusually perfect state of preservation, both the tissues of the 
phloem and of the inner and middle cortex. These will be 
described in detail below, in the hope that the knowledge of 
them may assist in the investigation of the vegetative axes ; 
it is not, however, assumed that the details to be described 
would necessarily apply for other species, as there is probably 
a considerable variety of structural minutiae in the different 
forms, while it is even possible that the details of the fertile 
and sterile axes might differ in the same species. 
The fossil is already well known by the description given of 
it by Robert Brown 1 , and it is extraordinary that investi- 
gators, having his description before them and the sections 
readily accessible, have not subjected them to fresh examina- 
tion in the light of the more recent advances in Palaeophy- 
tology. Graf Solms, referring to this fossil, quotes Schimper’s 
1 Linn. Trans. XX, p. 469, &c. 
