■ Il
'if 1 f!
many others besides, belonged to a group widely divergent from that of the true
Ferns, though related to them, and already presenting the essential characters of
Siiermophyta.
We will hrst direct our attention to the family Nenropteiideae, to which
Stui's remai'ke moi'e immediately refer. Simultaneously with his work, tlie late
M. R e n a u l t of Paris was able to yirove, by anatomical evidence, that the yietioles
of Xe n ro p t e r i s and Al e t h o p t e r i s wei'e identical with the iietrified fossils named
Myeloxylon by Bi'ongniart. a conclusion already suggested by M. G r a n d ' F u r y
some years previously (R e n a u l t 1883; G r a n d ’ F u r y 1877). In the mean time the
further fact had been yiroved, about 1880, by W e b e r , that the Myeloxylon petioles
were themselves borne on the remarkable and complex stems yilaced by Cotta in his
genus Alednl losa, a discovery which was only made public, in a convincing form,
as late as 189() (W e b e r and S t e r z e l 1890). AVe were thus placed in possession
of very comyilete data as to the whole vegetative structure of some, at least, ot the
Nenropterideae. I may be alloAved to illustrate the main points from the British
s])ccies Med u l l o s a ang lica, described by me in 1899, which is considerably simpler
than the Permian sjiecies of Germany and France, and shows the relation of the
different parts with great clearness (S c o t t 1899) (Fig. 1). The stem, in this species,
Fig. 1. A l e d u l l o s a angl i ca. Transverse section of stem with three leaf-bases (”M} ' e lo-
x y l o n “) attached. In the middle are the three steles. >< r//,,.
7—8 cm in diameter, usually contains 3 distinct vascular cylinders, or steles, each of
which has a solid axis of primary wood, surrounded by a zone of secondary wood
and bast produced by the activity of a S])ecial cambium (Fig. 2). From the outer
surface of the steles leaf-trace bundles are given oft', concentric in structure at
their base, but breaking up into a number of collateral strands, as they enter the
petioles (Fig. 3). The latter are thus supplied with a large number of foliar bundles.
only differing from those of I'ecent Cycads in the fact that, as a rule, the whole,
instead of merely the greatei' ])art, of the xylem is centripetally developed. In fact
Fig. 2. The tiiree steles and surronnding tissues enlarged. In each stele jirimary
and^ secondary wood is sliown. Leaf-trace bundles are also seen, x B'/,,.
Figs. 1 and 2. From a section kindly lent by Air. AV. II. SuTCi.iFFii, jihoto-
grajihed by Air. L. A. Bo o d l e .
the whole structure of the petiole, with its mechanically constructed hypoderma, and
nnmerous gum-canals, is strikingly like that of Cycad. The same comiiarison holds
good for the nsiially triarch adventitious
roots, which, m the English species, are
found springing from the stem, between
the leaf-hases.
The successive ramifications of the
rachis can be traced, and the leatlets prove
to be of the Al e t hop t e r i s type, and
very probably referable to the common
species A. lonchi t ica.
AVe thus see that in a Medu l l o s a
such as this a very I'emaj’kable combination
of characters is presented. In the primary
structure of the stem we have the essential
anatomical features of a dialystelic
Fig. 3. Two collateral leaf-trace bundles
in transverse section. / xylem; p x protoxylem;
ph phloem. X 35. From Scott, 1900. Scott
Collu 579.
Fern, while the form and venation of
the leaves are also altogether Fern-like.
On the other hand, the secondary tissues
of the stem, the anatomical strnctni'e of the petiole and I'achis, and the characters of