XIl] CHEIROSTROBUS 9 



tuting sporangiophores (fig. 117, A, B, f) or fertile divisions 

 of the sporophyll, expand distally into comparatively bulky 

 laminae ; each of these bears on its adaxial face four diagonally 

 placed outgrowths which form the short pedicels of very long 

 and narrow sporangia. The three lower segments — the sterile 

 divisions of the sporophylls — (fig. 117, A, B, s) are similar to 

 the upper set except in their greater length and in the kite- 

 shaped form of their distal laminae which are provided with 

 lateral lobes. The single vascular strand which supplies each 

 sporophyll is represented at It in fig. 117, B; at W the strand 

 has divided into four, the three upper bundles in the figure 

 supply the sterile segments and the single lower bundle 

 ultimately divides into three which supply the fertile segments. 

 A pair of blunt processes (fig. A, s) extend downwards over the 

 ends of the underlying fertile lamina and two slender prolonga- 

 tions extend upwards through several intemodes. 



An economical arrangement of the long and narrow sporangia 

 and of the sporophyll-segments between the axis and the 

 periphery of the cone is rendered possible by the interlocking 

 of the sterile and fertile segments by means of a groove in the 

 upper face of the latter for the accommodation of the former. 

 The sporangia are characterised by their unusually long and 

 narrow form : the length of a sporangium may reach 

 1 centimetre. In the structure of the wall the sporangia of 

 Gheirostrobus agree closely with those of Galamostachys^ and 

 Sphenophyllostachys. The spores are of one size only. The 

 vascular cylinder of the peduncle, originally described by 

 Williamson^ as the peduncle of a large Lepidostrobus (the cone 

 of Lepidodendron), is characterised by the presence of a short 

 radially disposed zone of secondary tracheids, a feature, as 

 Scott points out, which may extend into the axis of the cone. 

 It is noteworthy that the protoxylem elements are not always 

 external, but occasionally occur internal to one or two of the 

 outermost metaxylem tracheae : the usual exarch^ structure of 



1 Vol. I. p. 354, fig. 95, C. 



2 Williamson (72) PI. xliv. p. 297, figs. 29, 30. 



3 ' Exarch ' denotes that the protoxylem is on the outside of the primary 

 xylem ; ' endaroh ' that it is on the inner edge or in a central position ; ' mesarch ' 

 that it is internal, either near the inner or the outer edge of the metaxylem. 



