

148 



THE VASCULAR SYSTEM OF THE AXIS 



[CH. 



solenostelic {A), giving off at intervals a leaf-trace (B). Since its foliar gap 

 closes before the next leaf-insertion, only one is seen in any transverse 

 section. But where the internodes are shorter they overlap, so that more 

 than one appears (6^), and in the widely expanded adult stem several leaf- 



Fig. 138. Transverse sections of rhizomes of successive ages of Plagiogyria pycnophylla, showing tran- 

 sition from solenostely to dictyostely. A, a young solenostehc rhizome; B, same giving off a leaf- 

 trace; C, a larger rhizome with two leaf-gaps in section; D, vascular system of adult dictyostelic 

 rhizome, with the peripheral sclerenchyma omitted. Sclerenchyma dotted; xylem black. Note 

 the air-spaces (x) in D, and see text. (A, B, Cx 4; Dx 2.) 



Fig. 1 39. Vascular system of Pellaea rottmdifolia, showing the 

 departure of two leaf-traces (L.T.), and their relation to 

 the solenostele of the axis. (After Gwynne-Vaughan.) 



gaps are seen {D). Plagiogyria being a relatively primitive type, not far 

 removed from solenostely as Gwynne-Vaughan remarks, it demonstrates 

 the relation of .solenostely to dictyostely more clearly than it is seen in 

 more advanced Ferns, such as Dryoptei-is Filix-mas. Here the whole 



