360 



PART IV. CLASSIFICATION. 



(e.g. A. Phyllitidis) generally the lowest pair of pinnae of the 

 sporophyll alone bear sporangia ; these pinnse consist merely of the 

 nervature bearing numerous sporangia, and are erect on much 

 elongated secondary petioles : in Platy cerium alcicorne there is 

 a curious instance of specialisation ; the foliage-leaves are broad, 

 and closely appressed to the substratum, whereas the sporophylls 

 are erect, narrow, and branched. 



The sporangia are but rarely borne on the superior (ventral) 

 surface of the sporophyll (e.g. Olfersia cervina) ; more commonly 



FIG. 2U. Sori (s) of the most important groups of Leptosporangiate Ferns, all seen from 

 balow. A Pinna of Trichomanes sinuosum, one of the HymenophyllacesB : r projecting 

 placenta; s sporangia; i indu&ium ; at a half of the indusium is removed. B Pinna of 

 Davallia (Leucostegia) at s the one-valved indusium (i) is turned back. C Part of a leaf of 

 Pteris eerrulata -. 8 the sporangia; m the inverted margin. D Pinnule of Nephrodium at 

 s the indusium is removed, and at r the sporangia also. E Pinnule of an Asplenium at 

 a the indusium is turned back. F Pinna of Polypodium vulgare with naked sori at r the 

 sporangia are removed. (All a-e x 3 to 6.) 



on the margin (e.g. Hymenophyllacese, Dicksonia, Davallia) ; but 

 as a rule, on the dorsal surface, either near to the margin (e.g. 

 Pteris, Adiantum), or distant from it (e.g. Asplenium, Aspidium, 

 etc). They are usually developed in connexion with the nervature 

 of the sporophyll, but sometimes also from the intervening tissue 



