GROUP III. PTERIDOPHYTA : FILICIN^l ; LEPTOSPORANGIAT^. 389 



branches are borne on the flanks of the stem, and are frequently 

 (e.g. some Hymenophyllaceae) axillary in their origin. 



The leaves are for the most part foliage-leaves, though scaly 

 leaves are found on the subterranean rhizomes of Onoclea Stru- 

 thiopteris and Osmunda regalis, and in some cases the sporophylls 

 are more or less differentiated from the sterile leaves. 



The foliage-leaves are relatively large, sometimes entire (e.g. 

 Scolopendrium), but generally more or less deeply and repeatedly 



FIG. 257. Sori (s) of the most important groups of Leptosporangiate Ferns, all seen from 

 below. A Pinna of Tricliomanes sinuosum, one of the Hymenophyllaceae : r projecting 

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

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

 Pteris serrulata: s the sporangia ; m the inverted margin. D Lacinia of Nephrodium at 

 s the indusium is removed, and at r the sporangia also. E Lacinia 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 are x 3 to 6.) 



pinnately lobed or branched; sometimes dichotomously branched 

 (e.g. Platycerium, species of Schizaea). 



The leaves in all cases have apical growth ; the growing-point 

 has, in most of the orders, a two-sided apical cell, whilst in the 

 Osmundaceae the apical cell is tetrahedral. In Lygodium, where 

 the leaf is a climbing organ, the apical growth is long continued. 



