372 FILICALES [CH. 



fossil fern-stems with the habit and, in the main, the structural 

 features of recent tree-ferns. Persistent leaf-bases and sinuous 

 adventitious roots cover the surface of the stems : the vascular 

 system is of the dictyostelic type characteristic of Gyathea 

 (fig. 240, p. 313) and Alsophila. It is by the pattern formed by 

 the vascular tissue on the exposed surface of the leaf-bases that 

 Protopteris is most readily recognised : the leaf- trace has a horse- 

 shoe form with the ends curled inwards and the sides more or 

 less indented (fig. 277). The generic name Caulopteris is 

 used by some authors in preference to Presl's genus; but 

 Protopteris is more conveniently restricted to Mesozoic Cyathe- 

 aceous stems and Caulopteris to Palaeozoic stems, with the 

 internal structure of Psaronius (see Chap, xxiir.). Stenzel 



Fig. 275. A. Coniopteris arguta. (Fertile pinnae ; nat. size.) 

 B. C. Jnjmenophylloides. 

 A, from the Inferior Oolite of Yorkshire (British Museum) ; B, from Jurassic 

 rocks in Turkestan. 



applies Caulopteris to Mesozoic stems in which the leaf-trace 

 consists of several separate strands and not of a continuous band. 



Lower Cretaceous casts of tree-fern stems in the Prague 

 Museum have been described under the names Alsophilina and 

 Oncopteris ; the figures of the latter (fig. 276) given by Feist- 

 mantel' and by Velenovsky- show the petiole-bases arranged 

 in vertical rows and characterised by leaf-traces consisting of 

 two separate strands in the form of two Vs lying on their sides. 



Tree-fern stems described under various generic names are 

 not infrequently found in European Lower Cretaceous rocks: their 

 comparative abundance affords an example of striking changes 

 in geographical distribution since the latter part of the Mesozoic 

 epoch. The Cyatheaceae no longer exist in Europe and the 



1 Feistmantel (72). = Velenovsky (88). 



