LEAF 



291 



brown scaly hairs or r amenta, many of which are shed as the 

 blade unfolds ; they usually persist, however, upon the petioles 

 (Fig. 159, A, r.) and on the leaf-bases clothing the older parts 

 of the stem. As the leaf-rudiment produced behind the growing 

 point gradually develops, the axis of the lamina becomes coiled 

 after the manner of a watch-spring, and, in the case of compound 

 leaves, the individual portions become inrolled in a similar way 

 (Fig. 158, C). Each seg- 

 ment of the blade grows 

 by means of an apical cell, 

 which thus occupies a pro- 

 tected position within the 

 spiral formed by the ma- 

 turer parts. These features 

 are readily observed in a 

 young Bracken-frond, as it 

 emerges from the soil in 

 spring, and the prolonged 

 growth of its tip is evi- 

 denced by the retention of 

 the coiled character in the 

 uppermost portion, long 

 after the older basal -por- 

 tion is fully expanded. 



The development of Fern- FlG I59 ._ Entire fronds of A> Hart - s 

 leaves is usually very Tongue Fern (Scolopendrium vul- 



slow, the rudiment being gare) ; B, Polypody (Polypodium 



produced and undergoing vulgar*) ; and C, Maidenhair Fern 



, , r (Adiantum}. r., ramenta ; s., son. 



gradual enlargement for (AU three considerably reduced-) 



two or more years before 



the frond appears above the surface (cf. Fig. 158, B, 1, 



II, III). 



Not all Fern-leaves are as deeply compound as in the Bracken 

 (Pteris aquilina) or Lady Fern (Athyriumfilix-fcemina). Those of 

 the Polypody (Polypodium vulgar e, Fig. 159, B) and Hard Fern 

 (Blechnum spicant, Fig. 172), for instance, are simply pinnate, 

 whilst those of the Hart's Tongue Fern (Scolopendrium vulgare, 

 Fig. 159, A) are undivided. The venation is exceedingly char- 

 acteristic, the midribs of the leaves or pinnae, as the case may 



