Fossil plants, Vol. 2 : $b A text-book for students of botany and geologySeward, A. C. (Albert Charles)
Science
Fossil plants, Vol. 2 : $b A text-book for students of botany and geology
Seward, A. C. (Albert Charles)
Paleobotany
Evidence bearing on the existence of this family in Carboniferous
floras is by no means decisive. The generic name _Aneimites_ proposed
by Dawson[822] for some Devonian Canadian plants resembling species of
the recent genus _Aneimia_, and adopted by White[823] for a species
from the Pottsville beds of Virginia, is misleading. The Canadian
plants give no indication of the nature of the reproductive organs, and
the fronds described by White are, as he shows, those of a Pteridosperm
and bore seeds.
An examination of the suspiciously diagrammatic drawings published by
Corda[824] of the small fertile pinnules of a Carboniferous fern from
Bohemia, which he named _Senftenbergia elegans_, leads us to conclude
that the sporangia are almost certainly those of a Schizaeaceous
species. The small linear pinnules bear two rows of sessile sporangia,
singly as in recent Schizaeaceae and not in sori, characterised by
4–5 rows of regular annular cells (fig. 270, A) surrounding the apex.
It has already been pointed out that the apical annulus of recent
Schizaeaceae, though normally one row deep, may consist in part at
least of two rows. Zeiller[825] examined specimens of Corda’s species
and decided in favour of a Schizaeaceous affinity; he describes the
sporangia as 0·85–0·95 mm. in length, with 3 to 5 and occasionally only
two rows of cells in the apical annulus. Zeiller’s figures (fig. 270,
A) confirm the impression that Corda’s drawings are more beautiful than
accurate. Stur[826], on the other hand, who first pointed out that the
type-specimens of _Senftenbergia_ came from the Radnitz beds of Bohemia
and not from the Coal-Measures, convinced himself that the sporangia
have no true annulus (fig. 270, E). He describes them as characterised
by a comparatively strong wall and by the presence of a band of narrow
vertical cells marking the line of dehiscence, features which lead
him to assign the plant to the Marattiales, a group which seems to
have exercised a dominating influence over his judgment. In a later
publication Zeiller[827] replies to Stur’s criticism but adheres to
his original opinion. Solms-Laubach[828], while expressing himself in
favour of Marattiaceous affinity, recognises that Zeiller’s arguments
cannot be set aside.
The question must remain open until further evidence is forthcoming;
but it would seem that this Carboniferous type, not as yet recognised
in Britain, possessed sporangia having a distinct resemblance to those
of the Schizaeaceae, though this similarity does not amount to proof of
the existence of the family in the Palaeozoic era.
Palaeozoic floras may be described as rich in generalised types,
types foreshadowing lines of evolution, which in the course of ages
led to a sorting and a redistribution of characters. It may be that
_Senftenbergia_ is one of these generalised types.
• • • • •
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