390 



MOSSES AND FERNS 



CHAP. 



major part from the cap cell, which in all the forms becomes 

 much more developed than in any other Ferns, and from it 

 alone the apical annulus is derived. In Aiichjiia and Mohria 

 the tissue of the tip of the leaf adjacent to the sporangia grows 

 into a continuous indusium, which pushes them under to the 

 lower side. In Lygodiiiin (Fig. 224) each sporangium very 

 evidently corresponds to a single lobe of the leaf segment, and 

 has a vein corresponding to this. The pocket-like indusium 

 surrounding each sporangium grows up about it much as the 

 indusium of Trichomanes grows up about the whole sorus. 



sp. 



Fig. 228. — Alsophila Cooperi. A, section of the stipe, XiVz; B, cross-section of leaflet, 

 showing the sori, X20; C, open sporangium. 



The Cyatheace^ 



These are all Ferns of large size, some of them Tree-Ferns, 

 10 metres or more in height. They occur in the tropics of 

 both hemispheres, and some of them, e. g., Dicksonia antarctica, 

 are also found in the extra-tropical regions of the southern 

 hemisphere. They correspond so closely in all respects with 

 the typical Polypodiacece that, except for the slightly different 

 annulus, they might be placed in that family. In some forms, 



