THE STRUCTURE AND AFFINITIES OF DIPLOLABIS ROMERI (SOLMS). 733 



the other two groups — the Zygopteridese and the Osmundacew, though the petiolar 

 structure is not more primitive than that shown in the Osmundacem. On the whole, 

 the Boti-yopterideze, seems much nearer the osmundaceous type than are the Zygopteridese. 

 Indeed, the Zf/gopteridex seem to form a side branch from the main line of fern descent, 

 which did not survive into the Mesozoic period. The Osmundacese, on the other hand, 

 seem to have been a late branch, which was better suited to the. conditions prevailing 

 in Mesozoic and Tertiary times, and therefore they have persisted until to-day. 



In conclusion, I desire to express my thanks to the many friends who have given 

 me assistance in my work. I am especially indebted to Mr Arber, under whose super- 

 vision I have carried on my research. The Master and Fellows of Emmanuel College, 

 Cambridge, have supplied me with the machinery necessary for the preparation of sections, 

 and Professor T. M'Kenny Hughes has given me every facility in his laboratory at the 

 Sedgwick Museum, Cambridge. I have also to thank Professor James Geikie for 

 similar facilities in Edinburgh University and for communicating this paper. Finally, 

 1 am greatly indebted to Dr Kidston, Professor Gwynne-Vaughan, and Dr Scott for 

 many valuable suggestions and the advice they have given me in this research during 

 the past two years. 



My thanks are also due to the Executive Committee of the Carnegie Trust for a 

 grant to defray the cost of the illustrations in this paper. 



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(3) Bower, F. 0., On the Origin of a Land Flora, London, 1908. 



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(5) Cotta, B., Die Dendrolithen, 1832. 



(6) Kidston, R., and Gwynne-Vaughan, D. T., "On the fossil Osmundacefe," Parts i. to iii., Trans. Roy. 

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(9) Richter u. Unger, " Beitrag zur Palaeontologie des Thiiringer Waldes," Denkschr. d. k. k. Akademie 

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