550 CYCADOPHYTAN FRONDS [CH. 



and truncate, and the lamina may be entire or divided into a few 

 very unequal segments. The surface of the rachis is never com- 

 pletely covered by the lamina on the upper face of the frond and 

 is often characterised by transverse wrinklings, possibly due to 

 the presence of ramental scales. 



Some interesting xerophilous features have recently been 

 described by Halle^ in the lamina of Pterophyllum (Anomozamites) 

 marginatum, a Rhaetic species figured by Schenk and Nathorst 

 from Franconia and Scania. The pinnae were thick and succulent. 

 Stomata are confined to the lower surface and the edges of the 

 upper face of the lamina form a rounded curve causing the thick 

 upper cuticle to abut on the thinner stomatiferous lower cuticle, thus 

 producing in impressions the appearance of thickened margins. 



There is no satisfactory evidence as to the nature of the 

 reproductive organs or stems of the plants which bore fronds of 

 the type represented by P- Jaegeri (fig. 610) and other forms with 

 equal segments. A stem referred by Heer^ and by Leuthardt^ 

 to Pterophyllum was not found in connexion with leaves, and 

 there is the same absence of any convincing evidence in the case 

 of the imperfect specimens from the Keuper of Basel beheved 

 by Leuthardt to be male and female inflorescences. On the 

 other hand leaves of Anomozamites are known to have been borne 

 on comparatively slender stems with dichasial branching, and 

 the reproductive shoots are of the same general type as those 

 known as Bennettites. This discovery is due to Nathorst who 

 founded the genus Wielandiella^ on fertile stems with Anomo- 

 zamites fronds. Mr Thomas^ has recently obtained evidence 

 from Yorkshire Jurassic material pointing to a similar connexion 

 between Anomozamites fronds and Wielandiella stems. Ptero- 

 phyllum is further distinguished from Nilssonia by the folded 

 walls of the epidermal cells and by the presence of two crescentic 

 subsidiary cells (fig. 611, A) instead of the ring of cells which sur- 

 rounds the guard-cells in Nilssonia (fig. 611, B). Schenk^ figured 

 a few pieces of cuticle from fronds referred to Pterophyllum in 

 which the walls are more or less sinuous, but the cells of Ptero- 

 phyllum crassinerve Goepp.'' appear to have straight walls: this 



1 HaUe (15) p. 515, PI. xiii. figs. 18—20, 22. 



^ Heer (76) A. PI. xxxv. fig. 3. " Leuthardt (03) p. 20. 



* See page 463. » Thomas (13^) p. 237. 



» Schenk (67) A. Pis. xxxvii.— vni. ' Ibid. PI. xxxix. fig. 7. 



