SPOROPHYLLS 



309 



sides, exhibit practically no lamina (Fig. 173). In this connec- 

 tion it may be noted that in some tropical Ferns (e.g. Platycerium), 

 which grow aloft on the branches of trees (a habit commonly seen 



FIG. 173. A, Small part of a frond of the Royal Fern (Osmunda regalis), 

 showing sterile pinnules (below) and fertile pinnules (above). (About 

 half natural size.) (Original.) B, Single sporangium (after Luersen). 



in the Polypody in this country), the lowest leaves are modified 

 to form an oblique bracket by which humus is retained. 



A greater contrast between leaves and sporophylls is met 

 with in other groups of Pteridophyta, some of which are con- 

 sidered in the next chapter. 



