198 



GLEICHENIACEAE 



[CH. 



4, passes off with a shallow ad-axial pocket, as a C-shaped tract of xylem, 

 with internal phloem, and endodermis un-interrupted at the departure. Its 

 curve may enclose a mass of sclerenchyma. 



The C-shaped trace is frequently so strongly contracted in the lower part 

 of the petiole that the opposite curves may fuse, giving a pseudo-stelar effect 

 (Fig. 479). But as it passes up the petiole it is apt to open out with free 



Fig. 479. Transverse section of the base of the petiole of Gleichenia Fig. 480. Gleichenia line- 

 dicarpa, showing the pseudo-stelar structure resulting from contraction arts, series of transverse 

 of the horse-shoe-like xylem, till its margins fuse. (Photograph by sections of the rachis, 

 Dr Kidston from a section by Gwynne-Vaughan.) showing the extra-margi- 



nal origin of the pinna- 

 trace. (X4.) 



margins, as in other Ferns. The departure of the pinna-traces is extra- 

 marginal, as it usually is where the margins of the meristele are strongly 

 incurved (Fig. 480). Consequently the arrangement of the vascular tissues 

 at the base of the first pinnae may appeared involved : but comparison with 

 what is seen in LopJwsoria (Vol. i, p. 174, Fig. 170) shows that apart from 

 the lateral involutions of the trace, which are absent in Gleichenia, the method 

 is the same as that common for the Cyatheaceae. 



