In structure a cycadean sporangium recalls those of certain ferns (Marattiaceae, Osmundaceae and Schizaeaceae), but in the development of the spores there are certain peculiarities not met with among the Vascular Cryptogams. With the exception of Cycas, the female flowers are also in the form of cones, bearing numerous carpellary scales.
The first includes the Marattiaceae, Osmundaceae, Schizaeaceae, Gleicheniaceae and Matoniaceae; the second the Loxsomaceae, Hymenophyllaceae, Cyatheaceae and the Dennstaedtineae (a group including species placed in the Synopsis Filicum in Dicksonia and Davallia); while the remaining Polypodiaceae constitute the Mixtae.
15, G), Hymenophyllaceae and Osmundaceae, and on good grounds, so far as the external characters of the sporangia are concerned; our knowledge of most of the Ferns in question is, however, far too incomplete to justify us in asserting that they actually belonged to the families indicated.
In the case of the Osmundaceae there is good evidence, from anatomical characters, for tracing the family back to the Palaeozoic; their oldest members show a distinct relationship to the Botryopterideae, described in the next paragraph.
The family as a whole is of great interest, as presenting points of contact with various recent orders, especially Hymenophyllaceae, Osmundaceae and Ophioglossaceae; the group appears to have been a synthetic one, belonging to a primitive stock (the Primofilices of Arber) from which the later Fern families may have sprung.
The Osmundaceae, represented by a few forms of Palaeozoic age, played a more prominent part in the Mesozoic floras.
Specimens of Todites have been obtained from England, Poland, and elsewhere, sufficiently well preserved to afford good evidence of a correspondence in the structure of their sporangia with those of recent Osmundaceae.
Our knowledge of the anatomy of fossil Osmundaceae has recently been considerably extended by Kidston and Gwynne-Vaughan.
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