XXXVII] 



WILLIAMSONIA 



451 



of Cycadeoidea. The strobilus was probably borne at the apex 

 of a lateral branch given off from a stem covered with persistent 

 petiole-bases : there is no evidence that this was the case, but the 

 appearance of the ovoid cone suggests comparison with those of 

 Williamsonia gigas which were terminal on fairly long branches 

 and not partially hidden among the bases of fronds as in Cyca- 

 deoidea. It is, however, possible that the cone of Williamsonia 

 scotica is a lateral structure : this suggestion is based on the occur- 

 rence of a small branch or bud, which may be the apex of the 

 whole fertile shoot, given off from the cone-axis but only revealed 



FIG. 562. Williamsonia scotica. Transverse section; S, scales and megasporo- 

 phylls ; a, bract showing detached superficial tissue on the inner side. (ca. x 2.) 



in transverse sections. The interseminal scales, 2 mm. long and 

 0-23 mm. broad at the truncate distal end (fig. 563), are polygonal 

 in section and arranged as rosettes of 5 6 around each megasporo- 

 phyll (fig. 564, a section tangential to the peripheral layer of 

 scales and sporophylls). The megasporophylls, equal in length 

 to the scales, consist of a cylindrical axis bearing a terminal 

 megasporangium, an undifferentiated nucellus, enclosed in a 

 single integument prolonged as a micropylar tube above the 

 conical end of the nucellus (fig. 563, B, C, a). Fig. 562 represents 

 a transverse section through the cone showing the cylindrical 

 axis with its compact covering layer (fig. 563, A, s) of sterile and 

 fertile appendages, and beyond this sections of the enveloping 

 bracts embedded in a dense felt of long hairs. The tissue of the 

 axis, though very imperfectly preserved, shows occasional groups 



292 



