LEAF 



291 



brown scaly hairs or ramenta, 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 

 lea\-es, the individual portions become inrolled in a similar way 

 (Fig. 15S, 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 b}- the retention of 

 the coiled character in the 

 uppermost portion, long 

 after the older basal por- 

 tion is fully expanded. 

 The development of Fern- 

 lea\-es is usually ^'ery 

 slow, the rudiment being 

 produced and undergoing 

 gradual enlargement for 

 two or more years before 

 the frond appears above 

 II, HI). 



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

 (Pteris aquilina) 01 Lady Fern {Athyriuui filix-fcEiiiina). Those of 

 the Poh-pody [Polypodiitm viilgare, Fig. 159, B) and Hard Fern 

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

 whilst those of the Hart's Tongue Fern {Scolopendriiim vulgare, 

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

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



Fig. 159. — Entire fronds of A, Hart's 

 Tongue Fern [Scolopendriiim vul- 

 gare) ; B, Polypody [Polypodiitm 

 vulgare) ; and C, Maidenhair Fern 

 [Adianiiim). r., ramenta ; s., son. 

 (All three considerably reduced.) 



the surface (cf. Fig. 158, B, I, 



