PTER1POPHYTA. 



213 



1. The sporangia cover the entire lower surface of the leaf 

 (Tropical America and Asia). Acrostichum, Platycerium. 



2. Sori without indusia, circular or oval. Polypodium (Fig. 211 

 A}. The leaves are most frequently situated in two rows on the 

 dorsal side of the creeping rhizome, and fall off leaving a smooth 

 scar behind. P. vulgare, common in woods, on stones. (Phegu- 

 pteris also has no iridusium ; see page 214). 



3. The sporangia are situated in continuous lines just inside the 

 margin of the leaf. Pteris 1 : the sporangia form a continuous line 

 along the entire margin of the leaf (Fig. 211 C), which bends over 

 and covers the sporangia, forming a " false-indusium." Pteridium 

 has linear sori situated on a marginal vascular bundle, covered 

 by two linear basal indusia, of which the outer is bent over like 

 the edge of a leaf. P. aquilinum (Bracken; has a wide-spreading 



FIG. 211. Portions of leaves with sori. A Polypodium. B Aspidium. C Pteridium. I> 

 A sporangium of one of the Polypodiaceae : r the annulus ; s spores. 



rhizome with large alternate leaves, placed on opposite sides, at 

 some distance apart. Only one leaf is developed from each branch 

 every year. 



Adiantum (Maiden-hair) : sori on the underside of small portions of the edge 

 of the leaf, which are bent over (false indusium). Cryptogramme (Allosorus), 

 Cheilanthes. 



4. The sori are oval or linear, situated on one side of the 

 vascular bundle. Asplenium (Fig. 212 J.) ; sori linear; indusium 

 with one of its edges^ attached at the external side! A. ruta mura- 

 ria (Wall-Rue) ; A. septentrionale ; A. trichomanes. Athyrium : sori 

 linear cr curved; A. filix-fuemina (Lady-Fern). Scolopendrium 

 1 The former genus Pteris is divided into Pteris and Pteridium. 



