Fig. 18 



Stauropteris burntislandica : a, reconstruction of part of frond; 

 c, megasporangium {=Bensonites fiisiformis). Stauropteris 

 oldhamia: b, vascular system; d,. microsporangium. Botryopteris : 

 E, vascular strands of B. antiqua; f, petiolar strand of B. ramosa; 

 G, petiolar strand of B.forensis; h, vascular system of ^. trisecta; 

 I, reconstruction of part of the frond of an advanced species; 

 J, sporangium of B. globosa. 



(1, aphlebia traces; 2, dorsi ventral stele; 3, radial stele; 4, 

 dorsiventral petiole trace) 



(a, c, e, after Surange; b, g, Bertrand; d, f, Scott; h, Andrews; 

 I, Delevoryas and Morgan; J, Murdy and Andrews) 



were globose, up to 0-25 mm across, and had a multicellular 

 annulus that occupied almost half the surface area. 



A comparison of this early species with those of the Upper 

 Carboniferous and the Permian shows that there was a 

 trend in the evolution of the petiole trace towards a greater 

 degree of dorsiventrahty, together with an increase in the 

 number of protoxylems. Thus, Botryopteris ramosa (Upper 



125 



