214 



PTBRIDOPHYTA. 



(Fig. 212 if) : sori as in Asplenium, but situated in pairs across 

 the lanceolate, entire leaves. Each sorus is covered on the ex- 

 ternal side by an indusium, whose free edges are parallel and ap- 

 proach each other. S vulijare (Hart's-tongue). BlecUmim (B. tpicant, 

 Hard Fern ; the fertile leaves differ from the barren, the pinna? being narrower, 

 while tbe underside is almost entire'y covered with sori, arid hence they are of 



a much darker brownish hue than the barren ones) Ceterach : iudusium 



rudimentary or absent. 



5. Sori circular and covered by a shield-like, or reniform 

 indusium. Aspidium (Fig. 211 B) ; the leaves wither away and 

 leave no scar upon the root-stock. A. Jilix-mas (Male-Fern) ; A. 

 tt^inulosum. Phegopteris has no indusium, the withered bases of 

 the leaf-stalks are persistent ; P. dryopteris and P. polypodioides. 



6. The indusium is situated below the sori, and has the shape of 

 a one-sided scale (Cystopteris, Struthiopteris), or of a cup or cupule, 

 which in Woodsia is sometimes fimbriate (Fig. 212 C, !>}. 



/) 



FIG. 212. A Asplenium. B Scolopendrium. C Woodsia ; D single sorus of the same, 

 /v ( 'i/at/icu : the sporangia have fallen off in the upper sori. (All magnified.) 



7. The sori are situated on the margin of the leaf, and at the end of a 

 vascular bundle. Indusium, semi-cupjlar. Davallia. Principally tropical 

 species. 1 in S. Europe. 



This order is the greatest, comprising about 2,800 species, the 

 majority being perennial plants. A few are large, and known as 

 Tree-Ferns. 



As plants in conservatories and rooms the following are cultivated : species of 

 <;i/>nmjt (inline (tropical America), Lomaria, Nephrolepis, Pteris (P. scrrulata, 

 creticd). 



Officinal. Aspidium Jilix-mas, rhizome and the withered petioles. Species of 

 Alsophila and Cibotiuin give Penghawar Djambi. The rhizome of Pteridium 

 aquilinum, var. esculentuin, contains so much starch that it is used as food. 



The other orders of true Ferns deviate from the Polypodiaceae, especially in 



