THE PTERIDOPHYTA : FILICALES, THE FERNS 



563 



COMPENSATION 

 STRAND 



Fig. 571. — Pteridium aquilinum. Diagram of the 

 course of the vascular strands at a node. 

 Inner strands of rhizome and marginal lobes 

 of leaf trace shaded. A piece of the dorsal 

 outer strand of the rhizome is removed to 

 show the branching of the inner strand. 

 {After Tatisley and Lulham.) 



I 



J V 



A 



B 



C D 



Fig. 572. — Relation of leaf traces and leaf gaps to the stelar structure. In each case the 

 apex of the rhizome is to the left. A, Gleichettia flabellata. Protostele with no leaf 

 gap and solid leaf trace. B, Loxsotna cumiinghomii. Solenostele with isolated leaf 

 gap and C-shaped leaf trace. C, Pellaea rotiindi folia. Solenostele showing 

 departure of two overlapping leaf traces. D, Pteris elata var. karsteniana. 

 Polycyclic solenostele with part of outer stele removed to show leaf gap and 

 compensation strand in inner stele. (After Gzvynne Vaughan.) 



