XVIIl] 



ZYGOPTERIDEAE 



sJ. 



19 



Fig. 3x9. A^ikyropferis Grayi. Transverse section of stem, with axillary 

 shoot, and part of petiole. In the middle of the stem the 5-angled stele 

 is seen. /./., leaf-trace, about to give (jff the axillary strand; s.L, "scale- 

 leaf"; ax., axillary shoot of next node below; pet., part of petiole of the 

 subtending leaf. The small strand in the cortex to the right belongs to a 

 scale-leaf. ( x about 4.) From a photograph by Mr L. A. Boodle. Will. 

 Coll. 1919 A. (After Scott.) 



.singularly complex in many of its forms, from which pinna-traces were 



given off to supply the pinnae. These were arranged either in two ortho- 



stichies (Clepsydroideae, including Ankyropteris (?), Clepsydropsis, Astero- 



chlaena, and Asteropteris (?)) : or 



in four orthostichies (Dineuroi- 



deae, including Dineuron, Meta- 



depsydvopsis, Diplolabis, Botry- 



chioxylon (?), and Etapteris (Fig. 



320). 



In either case it appears that 

 the orientation of the pinnae was 

 not in the plane including the 

 rachis,as in modern Ferns. They 

 were expanded in planes trans- 

 verse to this, giving to the whole 

 upright leaf an almost radial 



symmetry, and a shoot-like as- Fig. 320. Diplolabis Romeri Solms. Diagrammatic 



nert This i'q an i"mr.r,rt-ant- t^oinf drawing showing the ramification of the primary 



pect. iniS IS an important pomt petiole, as it might be seen in a thick transverse 



in its bearing on foliar theory: section. /',/'= principal plane of symmetry; J/, 3/= 



r -^ ■ ^ ,1 , • median plane; a//^.= aphlebia-trace ; /?«Ai. = pinna- 



tor It IS clear that such an orien- trace. (From P. Benrand. After Gordon.) 



-iitiTV 



