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Mr. Kid s t o n 's new discovery confirms tlie suspicion which has been for some
time entertained, that a certain number of the so-called Fern-fructifications from the
Carboniferous rocks, will turn out to be in reality the microsporangia of Pteridospermeae.
At present we are not in a position to distinguish with any certainty between
the two kinds of organs. Where the fertile pinnae are considerably modified, as is
the case in Mr. K id s t o n 's Cros s o t h e c a , one may be inclined to suspect that a
Pteridosperm is in ipiestion, but tiiis argument lias little weight, for on the one hand,
welhmarked dimorphisin of the frond occurs in true Ferns, and on the other, the fertile
fronds of Pteridosiierms were sometimes very little modified, as we see in the case
of P e c o j i te r i s P luckene t i . It is probable that so far as the pollen-bearing organs
were concerned the Pteridosperms had not made much advance on the sporangial
apparatus ot true Ferns. In particular, it will be no easy matter to distinguish
between the iiolliniferous sori of Pteridosperms and the Marattiaceous synangia which
have so long been known on fronds of the Pe copt e r i s type. Even in the Mesozoic
Penn e t t i t e s , with female fructifications niore%omplex than those of any othei’ Gym-
nosperm, the pollen-bearing organs are compared by their discoverer AAAeland with
the synangia of Marattiaceae (AVie la n d 1899).
Mr. Kidston’s discover}®, at any rate, shows that the Cros s o t hec a s generally
were the male fructifications of Pteridospermeae, and in all probability of the special
family Lyginodendreae. Thus, not only is the position of several more species of
Sphenoj i tei ' is determined, but it ajipears that certain members of the form-genns
Pecop t e r i s are also involved, if M. Zeiller is right in referring the fructifications
of Pecopt e r i s exi gua, Ren. and P. p i n na t i f i d a , Gutbier, to Cros s o t h e c a
(Zeiller, 1900, p. 62). The former species in that case would be the only Cr o s so t
heca hitherto known with structure preserved; the sections of its sori as figured
by Renault (Renault. 1883, PI. 19, Figs. 13 — 18) are much like some of those
(e. g. Scolecopter is) commonly attributed to Marattiaceous Ferns.
If we now go on to consider, somewhat more closely, the systematic relations
of the Pteridospermeae, the first point which impresses itself on our minds is their
clear affinity with the Cycadophyta. This, indeed has long been recognized, as the
name Cycadofilices, hitherto applied to the group, indicates. Before anything was
known of the fructifications, the anatomical chai’acters both of the Lyginodendreae and
the Medulloseae pointed clearly to a position intermediate between the Ferns and the
Cycads. The seeds'of Lyg i no de nd ron (Lagenostoma) are evidently of the Cycadean
type, and the same holds good in a greater or less degree for the Palaeozoic seeds
generally with structure preserved, a large proportion of which doubtless belonged
to the Pteridosperms. In fact, so far as the seeds ai-e concerned, these plants had
already almost attained the rank of Cycads. An embryo, it is true, has never been
discovered; possibly its development was postponed till germination began, the resting
condition occurring at an earlier stage than in our modern seeds. It must, however,
be remembered that even in recent Cycads, the degree in which the embryo is developed
in the ripe seed is extremely variable, so that there is no sharp distinction in
this respect between the Palaeozoic seed-plants and their surviving allies.
Recent Cycads, as is well known, present clear indications of a relationship
with Ferns, as shown by the circinate vernation in many cases, by the habit of the
foliage in S t ange r i a , and by the grouping of the pollen-sacs in sori.
The ancient Pteridos])ermeae, however, stand incomparably nearer the Ferns
than the Cycads do. In the lattei' family both male and female fructifications assume, as
a rule, the form of a specialised cone; it is only in the female ,.fiower“ of Cycas itself,
that we find a more iirimitive condition, the foliaceons carpels, which often bear numerous
ovules, springing directly from the vegetative stem. In the Pteridospermeae all the
evidence goes to show that there was no approach to the diiferentiation of a cone —
the seeds, and doubtless the ])ollen-sacs also, were borne directly on compound fronds,
sometimes modified a little in the fertile ])arts, but in other cases practically identical
with the stei'ile leaves. In this respect the Pteridos])erms are by far the most primitive
of the known Seed-plants. To use a phrase employed in conversation by M.
van T ie g h em ,,ils sont des Phanérogames sans fieurs!“
In other woi’ds, these plants, while so fai' advanced in the organization of
the seeds themselves, remained at the level of Ferns as regards their sporophylls.
In habit indistinguishable from Ferns, as the exjierience of Palaeobotanists
has ])roved, the Pteridosiierms further retained many of the anatomical cliaracters of
their cryptogainic allies; in Lyginodendron, for example, at the present moment
the most completely known of all the family, the leaves were not merely those of a
Fern in form; they were also entirely Fern-like in structure. In He t e r a n g ium this
was also the case, and further, the pi'imary oi'ganization of the stem was that of a
Gleicheniaceons Fern. In Medul l os a, apart from the Fern-like habit, the primary
structure of the stem was that of the more complex Ferns. Thus the Pteridospermeae,
though they have proved to be seed-bearing plants, yet retain indisputable traces of
their origin from a common stock with the true Ferns. Hence they establish a definite
connecting link between tlie Cycadophyta and the Fern-phylum, though the actual
nature of the early Filicineae which gave rise to the Pteridosperms is still unknown.
That these ancestral forms stood nearer to the Ferns than to any other Cryptogamic
family appears certain; they may however have differed very considerably from Ferns
as we now known them.
Fossil evidence thus appears to have determined, in broad outline, the course
of descent of the Cycadophyta, a class of plants which, though now so reduced,
])layed a dominant part in the World’s Flora during the Mesozoic period.
Time will not allow us to enter fully into the important question how far
this conclusion holds good for the Gymnosperms generally. It may however be
pointed out that the characteristic Palaeozoic Gymnospermoiis family, the Cordaiteae,
though in many ways so far advanced, bear evident marks of an affinity with the
Pteridospermeae, as shown especially in the organization of their seeds, and the
anatomy of their leaves. The stems too, of the Cordaiteae, are connected with those