Fig. 276. Oncopteris Nettvalli. (After Velenovský; ¾ nat. size.)
Fig. 277. Protopteris punctata. (After Heer; very slightly reduced.)
Protopteris punctata (Sternb.). Fig. 277.
The earliest information in regard to the anatomy of this widely spread Lower Cretaceous fern we owe to Corda, who showed that the species agrees in essentials with existing tree-ferns. The English example described by Carruthers[920] from Upper Greensand beds in Dorsetshire (now in the British Museum) shows only the external features. The sandstone cast (14 cm. in diameter), of which a portion is seen in [fig. 277], was described by Heer from Disco Island (Greenland) as a Carboniferous species[921], but afterwards correctly assigned to the Cenomanian series[922] This species is recorded also from the Lower Cretaceous of Bohemia by Frič and Bayer[923] Among examples of petrified stems exhibiting a general agreement with Protopteris punctata are those described by Stenzel[924] from Turonian rocks in Germany. In one of these, Rhizodendron oppoliense Göpp., attention is drawn to branches given off from the stem stele which have a solenostelic structure in contrast to the dictyostele of the stem; also to the minute structure of the tracheae which appear to have their ends perforated, a feature shown by Gwynne-Vaughan[925] to be characteristic of the xylem elements of many ferns.
Fig. 278.
- A. Laccopteris polypodioides, Brongn. [From a specimen (39275) in the British Museum; slightly reduced.]
- B. L. Muensteri.
- C. Dicksonia (petiole stele).
- D. Onychiopsis Mantelli (fertile segments).
- E. Hausmannia Sewardi Richt.
- F. H. Kohlmanni Bicht.
- G, H. Protopteris Witteana, Schenk. (x, xylem; R, roots.)
(B, after Schenk; E, F, after Richter.)
Protopteris Witteana Schenk[926] ([fig. 278], G, H), a Wealden species recorded from Germany and England, represents a closely allied or possibly an identical type. The section of the stem (fig. H) shows the narrow vascular bands, x, of a dictyostele similar to that of recent Cyatheaceous tree-ferns and a form of meristele (fig. G, x) resembling that of P. punctata. Adventitious roots are seen in section at R (figs. G and H).