84 ORIGIN OF CORMOPHYTA [ch. 



other aphlebiae referred to the genus Rhacopkyllwn are extra- 

 ordinarily algal in aspect. Even ArcJweopteris itself retained not 

 only scaly emergences at the base of the frond but a large pair 

 of connate stipules (Fig. 28, 1, p. 56), no doubt originally of 

 branch origin like the fused branches of Cephalopteris. The 

 Archaeopteris type of leaflet also survived in the form of aphlebiae 

 well into UpiDcr Carboniferous times. Many of the smaller 

 Cyclopterid pinnules of Neuropteris are more or less Avedge- 

 shaped with a radiating nervation. In the larger and ? older 

 pinnules the shape changes to reniform or even orbicular, but 

 the same type of nervation persists. 



These facts afford another illustration of the law to which the 

 present writer^ in conjunction with Mr Parkin, called attention 

 some years ago, namely that corresponding stages in the evolu- 

 tion of the various members of a plant are not contemporaneous 

 in point of time. Here the foliar members clearly lag behind 

 other organs and are of more primitive form. 



It may be also pointed out that many genera of Carboniferous 

 Pteropsida exhibit in the dichotomies of their fronds traces of 

 their algal ancestry, as Potonie^ long ago pointed out. Such 

 genera as Rhacojyteris, Fig. 33, p. 61 (Lower Carboniferous), 

 and Mariopteris and many SphenoiDterids (Upper Carboniferous) 

 are cases in point. 



Primofilices^ . So far as we can see, all the fern-like plants of 

 the Devonian period were probably members of the Primofilices 

 and not Pteridosperms. We have failed to find any evidence of 

 the latter group and the remarkable absence of fossils obviously 

 of a seed nature has already been remarked upon here. However, 



1 Arber and Parkin (1907), p. 35. - Potonie (1895). 



' Prof., Seward (1910, p. 433) has taken exception to the term Primo- 

 fiUces on the ground that, according to his view, the name imphes "primary 

 or primitive ferns." This is an entire misconception for which we think no 

 justification will be found in the original paper by the writer (Arber, 1906) 

 in which the term was first used. So far as we know, the adjective jrritnus 

 has never been interpreted as 'primitive' whereas it may imply 'early,' 

 e.g. prima nox. The term Primofilices was and is intended simply to imply 

 "early ferns," and also to suggest the "Primary or Palaeozoic Age of the 

 race" (Arber (1906), p. 222). We fail to see any reason why this term should 

 be abandoned for the name Coenopterideae which Seward adopts, especially 

 as these plants do not appear to be generalised types. 



