GROUP III. PTERIDOPHYTA : FILICIN^E. 359 



The growth in length of the stem, is effected by a growing-point 

 with a single apical cell (with the occasional exception of 

 Osmunda) : the apical cell is, as a rule, a" three-sided pyramid 

 with its spherical base at the surface : but in Pteris aquilina it 

 is usually a two-sided lenticular cell, with its longer axis in the 

 dorso- ventral plane. 



The radial stems branch but little, least of all when the stem 

 is elongated, as in the Tree-Ferns ; and such branching as there 

 is appears to be mainly adventitious, the buds springing from the 

 bases of the leaves. In the dorsiventral stems there is normal 

 lateral branching, which takes place in the transverse plane : the 

 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 fojiage-leaves, though scaly 

 leaves are found on the subterranean rhizomes of Onoclca Stru- 

 thioptcris 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 

 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. 



The leaf arises from a single superficial cell of the growing- 

 point of the stem. When young it is strongly hyponastic (see 

 p. 211), so that, as it elongates and branches, both the main axis 

 of the leaf (phyllopodium) and the lateral branches become inrolled 

 upon themselves like a crosier ; in other words, the vernation is 

 circinate: as it grows older the growth becomes epinastjc, and 

 thus the leaf becomes expanded. 



In the great majority of these Ferns the sporophylls are simply 

 foliage-leaves bearing sporangia on the dorsal surface, b,ut in 

 certain cases they are more or less specialised. Thus, in Onocleq 

 Struthioptcris, the sporophylls are smaller than the foliage-leaves, 

 and have narrower pinnae : in the Hard Fern, Blechnum borealc, 

 the sporophylls are longer and have narrower pinnae than the 

 foliage-leaves : in Osmunda regalis the pinna? of the upper branches 

 of the sporophyll are reduced to little more than the midrib, the 

 pinnules' being represented by clusters of sporangia: in Aneimia 



