528 PTERIDOSPERMS, ETC. [CH. 



scale-leaves of considerable size (fig. 351) which occur in the 

 leaf-axils or as ochrea-like stipules on the fronds of Gunnera 

 (a tropical and subtropical Dicotyledonous genus) bear a very 

 close resemblance to some Palaeozoic Aphlebiae, e.g. Aphlebia 

 crispa (Gutb.). The recent and fossil scale-leaves may be 

 regarded as similar in function as in form; moreover the delicate 

 coiled fronds of Palaeozoic Pteridosperms or ferns, like those of 

 some recent flowering plants, may have been kept moist by a 

 secretion of mucilage. The pinnatifid stipules of Marattia 

 fraxinea (fig. 241, B, p. 317) resemble certain fossil Aphlebiae, 

 and the wrinkled surface of the recent stipules presents an 

 appearance similar to that which in some fossil forms has been 

 erroneously described as veining. It is not improbable that 

 mantle-leaves of such recent ferns as Polypodium quercifolium 

 (fig. 234, M, p. 303) are comparable with some fossil Aphlebiae 

 which may have served as humus-collectors for Palaeozoic 

 epiphytes. 



The filiform appendages on the petioles of the recent fern 

 Hemitelia capensis (fig. 235, p. 304) have often been compared 

 with the aphlebioid leaflets of fossil fronds. 



Potoni6 who has discussed the nature of Aphlebiae regards 

 them as vestiges of a once continuous lamina, which formed a 

 winged border to the branched axes of more primitive forms of 

 fronds. It is possible that the pinnules between the pinnae on 

 the rachis of Archaeopteris and the Cyclopteroid leaflets of 

 Neuropteris and Odontopteris may have the morphological 

 significance attributed to them by Potonie. In some cases 

 it is probable that the Aphlebiae, whether vestiges or not, 

 served the purpose of protecting either the whole frond or 

 individual pinnae. Aphlebiae, though especially characteristic 

 of Palaeozoic leaves, are occasionally met with in the form of 

 modified pinnules at the base of the primary pinnae on 

 Mesozoic ferns, e.g. in Coniopteris hymenophylloides^- 



In some fern fronds the lowest pinnule of each pinna 



differs in shape or size from the normal ultimate segments, 



but it would be almost affectation to extend the use of the 



term Aphlebia to such pinnules. The Jurassic species 



1 Seward (00) PI. xxi. fig. 1. 



