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
The drawing reproduced in fig. 138 is a copy of that of the
type-specimen: another specimen, named by Goldenberg, is figured
by Halle in his recently published paper. The leaves appear to be
distichous: no smaller leaves have been detected, though Halle is
inclined to regard the plant as heterophyllous. The sporophylls, borne
in slender terminal strobili, are smaller than the foliage leaves and
spirally disposed (fig. 138; smaller specimen). Halle succeeded in
demonstrating that some of the sporangia contained a single tetrad of
spores, each spore having a diameter of 0·4–0·5 mm. No microspores
were found, but it is clear that the species was heterosporous and
that it agrees with recent species in having only four spores in the
megasporangium.
_Selaginellites elongatus_ (Gold.). Fig. 135, B, D.
1855 _Lycopodites elongatus_, Goldenberg[230].
1870 _Lycopodium elongatum_, Schimper[231].
The shoots of this species resemble the recent _Lycopodium
complanatum_; they differ from those of _Selaginellites primaevus_ in
their long and narrow branches which bear two forms of leaf. The longer
leaves, arranged in opposite pairs, are slightly falcate; the smaller
leaves are appressed to the axis and have a triangular cordate lamina.
Another peculiarity of this species is the occurrence of sporangia in
the axil of the foliage leaves, a feature characteristic of the recent
_Lycopodium Selago_. In recent species of _Selaginella_ the sporophylls
are always in strobili. No microspores have been found nor the walls
of megasporangia, but tetrads of megaspores were isolated by Halle:
the spores have three radiating ridges (fig. 135, B) connected by
an equatorial ridge. Halle estimates the number of spores (0·45 mm.
in diameter) in a sporangium at 20 to 30. In size as in number the
spores exceed those of recent species and agree more nearly with the
megaspores of _S. Suissei_.
It would seem to be a general rule that the spores (megaspores) of the
fossil herbaceous species exceeded considerably in dimensions those
of recent forms and on the other hand were smaller than those of the
Palaeozoic arborescent species.
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