CYCADOFILICALES 



45 



PC b 



Fig. 47. — Trigonocarpum Parkinsonii: diagrammatic 

 transverse section through the micropyle at about the level 

 of pcb in fig. 46; for lettering see fig. 48. 



tions may occur in the nucellar tracheal mantle, which may be re- 

 placed by a vascular network or by distinct vascular strands. Later, 

 Scott and Maslen 

 (73) described two 

 species of Trigono- 

 carpum {T. Parkin- 

 sonii was probably 

 the seed of Medul- 

 losa anglica) from 

 the Coal-measures 

 (figs. 46-48) which 

 conform fully to the 

 Stephanos permum 

 type of structure, 

 in these cases the 

 three layers of the 

 testa being distin- 

 guished, and the 

 vascular strands oc- 

 curring in two sets 

 (an outer system in 

 the outer fleshy 

 layer, and an inner 

 system traversing 

 the periphery of the 

 free nucellus), both 

 distinctly cycadean 

 characters. The 

 inner vascular sys- 

 tem forms a " prac- 

 tically continuous 

 sheath" in the lower 

 part of the nucellus, 

 and is traceable 

 through the whole 

 length of the nucellus, almost to the base of the pollen chamber. A 

 remarkable feature of these winged seeds is the conspicuous micropylar 



m m 



Fig. 48. — Trigonocarpum Parkinsonii: diagrammatic trans- 

 verse section at about the level of mm in fig. 46; lettering for 

 figs. 46-48: sa, sarcotesta; I, its limiting layers; sc, sclerotesta; 

 mi, micropyle; it, remains of "inner flesh''; sab, sarcotestal 

 bundles; pc, pollen chamber; pcb, its beak; s, septum at bottom 

 of pollen chamber; ne, nucellar epidermis; nt, nucellar tracheal 

 system; mm, megaspore membrane; td, tracheal disk at chalaza; 

 chb, chalazal bundle; >•' and r', principal and secondary ridges; 

 all Xabout 3. — ^Maslen in Scotx (87). 



