217 
a New Fern from the Coal-Measures . 
be compared with the bundle-canals in the fossil petiole. In 
his description of the gum-canals of Angiopteris evecta , Frank 1 
speaks of two kinds, and gives an account of their develop- 
ment. Kuhn arrives at different results from those of Frank 
as regards the canal-development, and calls attention to the 
absence of epithelial cells 2 . This absence of a distinct 
epithelial layer lining the canal cavity in Marattiaceae 
agrees with the canal-structure in Rachiopteris Williamsoni. 
The existence of a stereome-group of elements in association 
with some of the larger canals in the fossil species is a character 
which we meet with in Angiopteris , Marattia and Danaea 3 . 
There is the further question as to the apparent absence of 
an endodermal layer in R. Williamsoni ; in recent Marattiaceae 
the vascular bundles of the petioles are often described as 
having no distinct endodermis. Van Tieghem 4 speaks of the 
steles of Marattiaceous petioles as having no well-marked 
{ plissements ’ on the walls of the endodermis, except in the 
case of Danaea. Leclerc du Sablon 5 points out that an 
endodermis exists in Angiopteris evecta, but its cells are only 
recognized after treatment with certain reagents. We may 
consider, therefore, that for purposes of comparison with fossil 
petioles, there is no endodermis in Marattiaceae, except, 
perhaps, in the case of Danaea. The preservation of the 
fossil vascular bundles is in this case so exceedingly good, 
that, if a typical endodermis were present, it would not be too 
much to expect that some indications of the usual characters 
might be detected in the mineralized tissue, especially in view 
of the fact that Hovelacque and Bower have recognized endo- 
dermal cells in Lepidodendroid axes. 
On the whole, then, I regard Rachiopteris Williamsoni as 
a fern-petiole, which agrees in the histological details of 
structure more closely with the petioles of Marattiaceae than 
1 Beitrage zur P flanzenphysiologie, Bd. ii. 1868, p. 112. 
2 Kiihn, loc. cit. pp. 32, 51. 
3 My thanks are due to Prof. Bower for specimens of this genus. 
4 Trait. Bot. Vol. ii. 1891, p. 1388. 
5 Ann. Sci. Nat., Bot., Ser. II. Vol. xi. 1890, p. 12, PI. II, Figs. 29-31. 
Q 
