CH. XLIV] 



BLECHNUM 



169 



BLECHNUM SPICANT (L.) Wither 

 Perhaps the best intermediate illustration is provided by the familiar Hard Fern, 

 Blechmim spicant. This common species is the only representative of Bleclminn native in 

 North Temperate lands. Its very sclerotic upright stem contains a vascular system with 

 binary leaf-traces, conforming to the type, though simpler than in B. tabiclare. Its leaves 

 are dimorphic. The general character of the fertile pinnae is seen in Fig. 691, A. Here 

 there is a narrow flange on either side, so that the coenosori appear to be slightly intra- 

 marginal. If the tip of the pinna be cleared, the sori and their vascular relations are visible 

 as in Fig. 692, 9. Short vascular twigs pass into the flange : this is an advance on the 

 species previously described. The sori, shown as continuous shaded tracts, stop some 

 distance from the apex. A vascular commissure runs below each, connecting the veins : 

 but this also stops short where the sorus ends. The relation of the commissure to the veins 

 suggests very strongly that it is actually composite, being built up from individual 

 extensions of the anadromic branches of the furcate veins. This was the view held by 

 Mettenius {Fil. Hort. Lips. p. 60, Taf v. Fig. 5). 



A 



Fig. 691. Blechmim spicant (L.) Wither. ^ = two segments from the upper part of an 

 immature fertile leaf: the "indusium" and sori of the lower pinna have been removed 

 halfway up from the base to show the nervation. ( x 5.) j5 = half of a transverse section of 

 a fertile pinna, after Mettenius. /= "indusium." ;- = receptacle with underlying commissure 

 cut through. The larger vascular strand is the mid-rib of the pinna. ( x 30. ) 



The development of the fertile pinna of BlecJmum spicant begins in the usual way, by 

 alternate cleavages of marginal cells (Fig. 692, 10, a). But the marginal cells take their 

 place quite definitely at the apex of the flange, which is here of larger size proportionately 

 than in the previous examples (Fig. 692, 10, b-d). The whole flange is referable in origin 

 to them. But soon a stronger growth appears on the abaxial face distinctly back from the 

 margin ib). It consists of a broad convex weal, and the slope of it which faces the mid- 

 rib obliquely soon shows deeper cells : these, undergoing segmentation, produce sporangia, 

 with slight signs of a gradate sequence {c, d). On the side away from the mid-rib the 

 "indusium" arises; it is relatively late in origin, and remote from the margin. The late 

 appearance and intra-marginal position mark B. spicaitt as farther removed from the 

 condition of Matteuccia than the species previously described. But notwithstanding this 

 the essential identity of the several parts within so natural a genus is beyond doubt. 

 B. cape?jse (L.) Schlecht and B. gibbum (Lab.) Mett. give similar results (Fig. 692, 10, a-c). 

 These species also show instability in their dimorphism, with widening out of the flange in 

 fertile pinnae, so as to form a broad expanse with an extensive venation of its own. 



