Proceedings of the Linnean Society of London - University Library

lilNNEAN SOCIETY OF LO>'DO:!f. 55
Botrvopteridea; constitute one family of the Priiiiofilices, aud
others will prohably be distinguished iu the near future.
The origin of the LeptosporangiatcTe from the Primofilices is clear.
This group began to differentiate at the close of the Palteozoie
period. Possibly some of the Sphenopterid fronds of the Carboniferous
aud Permian rocks, bearing annulate sporangia, were the
earliest offshoots in this direction. In the true Mesozoic floras
(Ehpetic, Jurassic, and Wealden) the various families became
marked out, and there is abundant evidence that the Leptosporangiatse
then formed one of the dominant or ruling types of
Mesozoic vegetation.
On the other hand, the question may well be asked, Is there any
trustworthy evidence of the existence of the Eusporangiatae in
either the Palaeozoic or truly Mesozoic floras ? In neither is there
any evidence at all of the Ophioglossacea?, and the only instance
of possible Mesozoic Marattiaceous fronds with which I am
acquainted are three in number, and all of EbiBtic age. In two
species of Tcenioptcris (including the typical Rhaetic species
T. Jlilnstej'i) sporangia, resembling those of the modern Marattia,
have been found on certain fronds while in Dano'opsis, another
related genus, the synangia more closely resemble those of Dancea.
The suspicion is not wanting, however, that the fi'onds of Tamiojiteris
may have been those of a Cycad rather than a Pern.
In the Palaeozoic rocks, we find a plexus of fronds of the
Sphenopterid and Pecopterid type, bearing exannulate sporangia,
arranged independently in the sorus, or united to form synangia.
These have been generally regarded as of Marattiaceous aftiuity.
The great difficulty, at the present moment, is to decide as to the
true nature of these fronds. Did they belong to true homosporous
Ferns, or were they the male fronds of Pteridosperms ? On the
present evidence, I am inclined to think that a large number,
though not necessarily all, will eventually pi'ove to fall under the
latter category. "We already know that one Pecopteris (P. PlucJceneti),
though not a very typical member of the genus, belonged
to a Pteridosperm. Also the male frond of the Benuettiteae, a
group descended from the Pteridosperms, is known to have borne
sporangia not unlike those of the Palaeozoic Pecopterids and the
modern Marattiacea;.
The anatomy of the tree-fern, Psaronlus, affords the most trustworthv
evidence, at preseut, of the existence of the Eusporanf/iatce
in Palaeozoic times ; though there would appear to be little to
indicate that this group ever attained to the position of a dominant
or ruling type in either the Palaeozoic or truly Mesozoic floras.