TRANSACTIONS OF SECTION K. 1007 
traceous character. Hence, for a good many Carboniferous and Permian forms 
there is not the slightest doubt as to their fern-nature, and we can even form an 
idea of the particular group of Ferns to which the affinity is closest. 
I will say nothing more as to the true Ferns, though they present innumerable 
points of interest, but will pass on at once to certain forms of even greater import- 
ance to the comparative morphologist. 
A considerable number of paleozoic plants are now known which present 
characters intermediate between those of Ferns and Cycadee. I say present inter- 
mediate characters, because that is a safe statement; we cannot go further than 
this at present, for we do not yet know the reproductive organs of the forms in 
question. 
In Lyginodendron, the vegetative organs of which are now completely known, 
the stem has on the whole a cycadean structure ; the anatomy, which is preserved 
with astonishing perfection, presents some remarkable peculiarities, the most 
striking being that the vascular bundles of the stem have precisely the same 
arrangement of their elements as is found in the leaves of existing Cycads, but 
nowhere else among living plants. The roots also, though not unlike those of 
certain ferns in their primary organisation, grew in thickness by means of 
cambium, like those of a Gymmnosperm. On the other hand, the leaves of 
Lyginodendron are typical fern-fronds, having the form characteristic of the 
genus Sphenopteris, and being probably identical with the species S. Haninghaust. 
Their minute structure is also exactly that of a fern-Srond, so that no botanist 
would doubt that he had to do with a Fern if the leaves alone were before him. 
This plant thus presents an unmistakable combination of cycadean and fern- 
like characters. Another and more ancient genus, Heterangiwm, agrees in many 
details with Lyginodendron, but stands nearer the ferns, the stem in its primary 
structure resembling that of a Gleichenia, though it grows in thickness like a 
eycad. These intermediate characters led Professor Williamson and myself to 
the conclusion that these two genera were derived from an ancient stock of Ferns, 
combining the characters of several of the existing families, and that they had 
already considerably diverged from this stock in a cycadean direction. I believe 
that recent investigations, of which I hope we shall hear more from Mr. Seward, 
tend to supply a link between Lyginodendron and the more distinctly cycadean 
stem known as Cycadoxylon. 
Heterangium first appears in the Burntisland beds, at the base of the carboni- 
ferous system; from a similar horizon in Silesia, Count Solms-Laubach has de- 
scribed another fossil, Protopitys Bucheana, the vegetative structure of which also 
shows, though in a different form, a striking union of the characters of Ferns and 
Gymnosperms. Count Solms shows that this genus cannot well be included amone 
the Lyginodendrez, but must be placed in a family of its own, which, to use his own 
words, ‘ increases the number of extinct types which show a transition between the 
characters of Filicine: and of Gymnosperms, and which thus might represent the 
. descendants in different directions of a primitive group common to both.’ ? 
Another intermediate group, quite different from either of the foregoing, is 
that of the Medulloseze, fossils most frequent in the Upper Carboniferous and Per- 
mian strata. The stems have a remarkably complicated structure, built up of a 
number of distinct rings of wood and bast, each growing by its own cambium. 
Whether these rings represent so many separate primary cylinders, like those of an 
ordinary polystelic Fern, or are entirely the product of anomalous secondary 
growth, is still an open question, on which we may expect more light from the 
investigations of Count Solms. In any case, these curious stems (which certainly 
suggest in themselves some relation to Cycadex) are known to have borne the 
_ halal as Myeloxylon which have precisely the structure of cycadean 
petioles. 
Renault has further brought forward convincing evidence that these Myeloxy.«n 
petioles terminated in distinctly fern-like foliage, referable to the form-genera 
' Bot. Zeitung, 1893, p. 207. 
2 Seward, Annals of Botany, vol. vii. p. 1. 
