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REPRODUCTIVE STRUCTURES. 



The curvature of the free rachides one readily imagines from the behavior of 

 those of the once-inflexed foliage fronds of Zamia or the fertile carpels of Cycas. 

 No doubt the drooping pinnules moved forward about the same time that the syn- 

 angia began to dehisce. There is also a strong presumption that the pinnules were 

 fugacious, leaving their scars on the rachides at the same time that the disk split 

 away from its axis. This would account for Williamson's statements concerning 

 the disk markings seen in figure 78 (202, fig. 2, pi. 53), with the exception of 

 the supposed seeds. Dehiscent fern pinnules would leave such scars, and in spite 

 of the fact that other observers have not confirmed Williamson's statements, it 

 would seem quite probable that he did see sufficient evidence to justify most 

 of the details he has figured. The general appearance which one of the present 



ST. 



S.50O. 



Fig. 80.— Cycadeoidea dacotensis. Bundle systems of the ovulate cone and fronds of bisporangiate strobilus. 



a. Transverse section of the woody cylinder of receptacular region of cone of strobilus in bisporangiate stage, showing disposition of bundles. 



mainly indicated by groups of scalariform cells believed to be the centripetal elements of a mesarch system like that of Lyginodendron. 

 ■ 1 50. For the corresponding longitudinal section see (b) f from larger ovulate cone, which has doubtless shed its staminate dislc. 



b. Longitudinal section through the woody cylinder of the receptacular region of the cone shown on Plate XL. '■' 100. A series of scalari- 



form tracbeids is seen to traverse a coarse secondary granulation of the siliceous gToundmass. These tracheids are similar to those of the 

 central ovulate cone of the bisporangiate axes actually bearing staminate disks, and are possibly centripetal wood only, corresponding to 

 that of the mesarch stem bundles of Lyginodendron. The preceding figure is that of the transverse section of the corresponding cylinder 

 of a cone from a bisporangiate axis in which the tracheids are much younger and smaller. 



c. Transverse section through the superior region of the rachis of a sporophyll, showing xylem elements of bundles only. As in the preceding 



bundles from ovulate cones, mainly scalariform elements are preserved. • 60. For entire sporophyll bundle patterns see figure 74. 



disks would present, if its pinnules were to dehisce, is shown in figure 79, and the 

 striking similarity to Williamson's figure requires no further comment in the 

 absence of precisely the specimens Williamson originally had before him. The 

 French specimen, figure 76, is also suggestive in the present connection. It appears 

 that the Williamsonia disks were borne on long peduncles. At least it is clear that 

 if any of these strobili were borne on peduncles longer than the old leaf bases, the 

 decidedly flower-like appearance indicated in figure 54 would be presented at 

 maturity, and that such flowers would scarcely be preserved at all, unless as detached 

 and isolated imprints. 



