THE PTERIDOPHYTA : FILICALES, THE FERNS 



525 



Protoxylem 



Phloem 



Metaxylem 



Fig. 522. — Osmunda regalis. Transverse section of 

 the root showing diarch xylem. 



Anatomy of the Leaf 



The base of the petiole forms part of the structure of the stem and has 

 already been described. As the leaf trace ascends the petiole it becomes 

 broader and opens out into a C-shaped band, with the arms directed adaxially 

 and the edges incurled (Fig. 523). The protoxylem divides into several 

 groups, arranged along the concave face, alternating with groups of mucilage 

 cells. A narrow phloem mantle and a continuous endodermis surrounds the 

 whole strand. When a pinna trace is given off the petiolar strand broadens 



Fig. 523. — Osmunda regalis. Transverse section of the petiole 

 showing C-shaped vascular strand. 



