Johnson — Is Arcliceopteris a Pteridosperm ? 123 



rachis from each pinnule (PI. V., fig. 5). In some cases it looks as if one or more 

 main veins are present ; but this is due to the fact that some of the pinnules 

 were in a state of decay, rotting in the water when fossilised, and the 

 bundles of the skeleton of the leaf became crowded together in the process. 

 Neither in the pinnules nor rachis (primary or secondary) is there any sign 

 of a main ■vein. As already mentioned, M. Brongniart first observed that the 

 primary rachis carries not only the pinnse, but between them, usually opposite 

 one another and occasionally in two pairs, pinnules in all respects comparable, 

 except for position, to the ultimate pinnules of the pinnse described. 

 Occasionally I have found such a pinnule replacing a pinna, whether sterile 

 or fertile, and even doing this alternately on either side of the rachis, both 

 towards the base and the apex of the frond. Such inter-pinnate pinnules or 

 rachidial pinnules, as I prefer to name them (called deeursive pinnse by 

 Potonie, and " Zwischen-Fiedern " by Nathorst), are not confined to 

 Archseopteris, though a constant feature of it. Tliey are of the same nature 

 as the Aphlebise of Potonie, who regards such structures as ancestral 

 remains, indicative of a state when tlie rachis was clothed its whole length 

 with a continuous lamina. The Aphlebise in this interpretation would bear 

 the same relation in time to the general frond as the cotyledons and 

 embryonic leaves of a flowering plant to its adult foliage. If really 

 ancestral, they are of distinct taxonomic value. The basal pairs of rachidial 

 pinnules, along with the stipulate base already mentioned, are of interest in 

 this connection. 



Arcliceopteris hiiernica is not recorded as such outside the British Isles. 

 Wlieu Nathorst first found the Archseopteris deposit on the south-east shore 

 of Bear Island in 1898, he recorded as A. hibernica the form, now made 

 known by him, in its sterile state only, as A. intermedia Nath. In its long 

 and more erect pinnse A. intermedia suggests A. Roemeriana, but in its lobed 

 pinnules differs from it, and approaches A. fimbriata Nath., with its still 

 narrower but distinctly laminated laciniate pinnules. 



Fertile Fronds of Arcliceopteris hibernica. 



In general features the fertile frond (PI. lY.) agrees with the purely 

 vegetative one. Some of its pinnse, usually the sub-basal ones, may be 

 formed almost completely of fertile pinnules. Often, however, the basal 

 and apical pinnules of a fertile pinna are sterile, and the central pinnules 

 only are fertile, and even of these pinnules the apical part of each may be 

 vegetative. Thus the tendency is for the non-apical parts of the central 

 pinnse of the frond to become fertile. Sterile pinnules with marginal 



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