XIl] 



SPHENOPHYLLUM 



the base and forming a narrow flange encircling the axis. 

 Each bract, the base of which forms part of the narrow collar 

 surrounding the axis, consists of two lobes, ventral and dorsal, 

 divided palmately into several (sometimes four) segments or 

 sporangiophores (fig. 115). Each sporangiophore terminates 

 distally in an oblong or oval lamina bearing two sporangia on 

 its adaxial face (fig. 114). The space between the axis and the 

 periphery of the cone is thus occupied by crowded peltate 

 laminae, each with its pair of sporangia. A single vascular 

 bundle supplies each sporangiophore and bifurcates in the 



Fig. 115. Sphenophyllostachys fertilis (Scott). (After Scott.) Diagram of a 

 single sporophyll as it would appear in a transverse section of the cone ; 

 showing one lobe (dorsal or ventral), ax, part of axis to which the 

 sporophylls are attached. 



distal lamina into two branches which extend to the bases of 

 the sporangia. The sporangia agree in structure with those of 

 other species of Sphenophyllum : the spores are of one size and 

 elliptical, characterised by the presence of several sharp ridges 

 or flanges encircling the spore-wall in the direction of the major- 

 axis. Sphenophyllostachys fertilis differs from all previously 

 recorded types in the absence of sterile bracts. The appendages 

 of the cone-axis are all fertile, a striking contrast to the 

 differentiation into protective and sporangia-bearing bracts which 

 constitutes a constant feature in the cones of Sphenophyllum 

 and Calamites. It is possible, as Scott suggests, that the 

 absence of sterile segments is the result of modification of the 



