( 711 ) 



XXIV. — On the Structure and Affinities of Diplolabis romeri (Solms). By W. T. 

 Gordon, M.A., B.Sc, B.A., Falconer Fellow of Edinburgh University, Lecturer 

 in Palaeontology, Edinburgh University. Communicated by Professor James 

 Geikie, D.C.L., LL.D., etc. (With Four Plates.) 



(MS. received November 4, 1910. Read December 20, 1909. Issued separately February 4, 1911.) 



CONTENTS. 



PAGE 



Introduction 711 



General Structure . 715 



Histology :— 1. Of the stem 719 



2. Of the petiole . . . . . 720 



3. Of the root .... 726 



PAGE 



Summary 727 



Diagnosis 728 



Conclusions and General Considerations . . . 728 



Bibliography 733 



Explanation of Plates 734 



Introduction. 



Probably the commonest type of foliage among the impressions of Carboniferous 

 plants is one which simulates that of our living ferns. These palaeozoic fronds were 

 originally believed to belong to the true ferns, but recently some of them have been 

 taken from this group and included in the Pteridospermese. There remain, however, 

 a large number of fronds the true affinities of which are yet doubtful. Thus, though 

 there are still a considerable number of species which belong to the ferns, the number 

 of doubtful examples and of those now definitely known to be pteridospermous far 

 exceeds the number of those attributed to the Filices. Indeed, we cannot now consider 

 the latter group to have been dominant during the Carboniferous epoch. 



What is true of the carbonised impressions is equally true of the petrifactions. In 

 the petrified specimens, however, it is rather easier to determine which are likely to 

 belong to the fern group and which are not. It was among these petrified examples, 

 indeed, that the first indications of the Pteridospermeae (Cycadofilices) were detected, 

 and it was also from petrified specimens that the seed habit among fern-like plants was 

 demonstrated. 



There are several well-marked genera among the ferns # of Carboniferous times, 

 and recently a great deal of attention has been devoted to this group. Mr Arber (1) 

 has instituted the group of the Primojilices to contain the ancient palaeozoic ferns 

 such as the Botryopterideae and Zygopterideae. Dr Scott, Professor Bower, and others 

 have discussed the relation of palaeozoic ferns to recent forms, showing how they may 

 be classified, and that that classification is in harmony with the geological evidence. 



* The Botryopterideae, though very different from modern ferns, are generally classed with the Filicales. Under 

 that name (Botryopterideae), two very distinct orders are placed, viz. : — Botryopteris and Zygopteris. The differences 

 between these, however, seem too great to allow of their inclusion in the same order. In what follows I use the 

 terms Botryopterideae and Zygopterideae as representing orders which are as distinct from one another as, say, that of 

 the Osmundacese is from either of them. 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART. IV. (NO. 24). 105 



