XXXVIl] WILLIAMSONIA 433 



face of Williamson's lenticular disc is characterised by a series 

 of spoke-like radiating ridges (fig. 547, A') between which are 

 less distinct radially disposed lines, and at the periphery there are 

 impressions (fig. 547, A"), continuous with some of the radiating 

 ridges, of the terminal shields of interseminal scales. In fig. 547, 

 drawn from one of the original specimens described by Williamson, 

 these features are shown at A' and B : fig. A' represents the 

 circular area, which is at right-angles to the axis of the flower, 

 in surf ace- view. In the centre of this circular area is a depres- 

 sion ending in a short papilla surrounded by a narrow basal rim : 

 this feature is shown on a cast of the specimen represented 

 in fig. 547, B. In this case Williamson's corona is seated on 

 a very short axis whereas in fig. 547, C, also from one of 

 Williamson's specimens, the corona forms the apex of a longer 

 pyramidal axis. Wieland 1 regarded the circular area seen in 

 fig. 547, A, as the impression of the apical portion of a bi- 

 sporangiate strobilus, the ridges marking the edges of the incurved 

 distal portions of microsporophylls bent over the apex of the 

 ovulate cone (cf. fig. 513), and he interpreted the polygonal 

 depressions at the periphery (fig. 547, A'') as those of sori, an 

 interpretation entirely different from that of Lignier. The latter 

 author 2 in part reasserted his opinion but modified it as regards 

 the meaning of the ridges on the circular area, agreeing so far with 

 Wieland as to consider them as having been formed by the folded- 

 over rachises of microsporophylls attached as a concrescent collar 

 to the base of the ovulate cone. This interpretation does not, 

 however, explain the relation between the radial striations on 

 the circular area and the polygonal impressions at its periphery. 

 Wieland still dissents from Lignier 's opinion and suggests that 

 the circular area has not been demonstrated to belong to the 

 apical end of a flower. Fig. 547 shows that its position is apical. 

 Fig. 548 represents Lignier's view as to the nature of the rim 

 surrounding the apical mammilla : he suggested that several 

 interseminal scales borne at the apical region of the receptacle 

 were concrescent and formed linear bracts the edges of which 

 are represented by the main ridges in fig. 547, A'. These con- 

 crescent scales bent upwards and were closely applied to or perhaps 



1 Wieland (06) p. 152. 2 Lignier (07); Wieland (11) p. 462. 



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