214 



PTEEIDOPHYTA. 



(Fig. 212 B} : 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'othe'r. S. vidgare (Hart's-tongue). Blechnum (B. spicant, 

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

 while the underside is almost entire'y covered with sori, and hence they are of 

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

 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. filix-mas (Male-Fern) ; A. 

 spinulosum. 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 0, D). 



FIG. 212.^! Asplenium. B Scolopendrium. C Woodsia ; D single sorus of the same. 

 E Cyathea : 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-cupnlar. 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 

 Gymnogrartime (tropical America), Lomaria, Nephrolepis, Pteris (P. serrulata, 

 cretica). 



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

 Alsophila and Cibotium give Penghawar Djambi. The rhizome of Pteridium 

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



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



