XLiv] ACROSTICHOID DERIVATIVES I75 



Stenochlaena J. Sm. 



5. sorbifolia (L.) J. Sm. is a species widely spread throughout the tropics, 

 and notwithstanding vicissitudes of nomenclature it may properly be placed 

 as a Blechnoid derivative. It is a widely climbing Fern with extraordinary 

 variability of leaf-form (Fig. 697). A Pimpinelloid form of leaf is found in 

 the lower parts of the plant, resembling those of B. filiforme (A. Cunn.) 

 Ettingsh.: but in the climbing region the sterile leaves are commonly of the 

 usual Blechnoid type, while the fertile also resemble those of species of 

 Blechmivi, except that the soral region is wide and everted at maturity, 

 exposing very numerous sporangia spread over its surface. As further 

 illustrating the variability of leaf-form in the genus there is a vivid description 

 by Karsten of a Moluccan species, referred by Christensen to S. aaileata 

 (Bl.) Kze., where there are two types of sterile leaves in the climbing region, 

 one of which corresponds to the sterile leaves of 5. sorbifolia, the other is 

 closely appressed to the surface of the support, and Karsten ascribes to them 

 a water-collecting function (see Vol. I, Fig. 42). 



Notwithstanding the elongated internodes of the climbing stem of 5. sorbi- 

 folia, the structure accords with that usual in the Blechnoids (Fig. 698). Roots 

 formed on the side in contact fix it to the support, while rhizoid-like hairs 

 also assist. The periphery of the roughly polygonal section is sclerotic, 

 interrupted here and there by lacunar tissue. The vascular system is clearly 

 a modification of the Blechnuin type, the meristeles being large, with very 

 narrow leaf-gaps, opposite to which the usual root-traces are seen (Nos. 2 

 and 4). The leaf-traces consist usually of four to six strands forming a 

 horse-shoe, which is thus of advanced t)'pe as compared with Matteitccia, 

 B. tabulare, or B. spicant. All this accords with the position of Stenochlaena 

 as a derivative type. 



The youngest stages of the fertile pinnae of Stenochlaena have not been 

 observed: but sufficient has been made out to give a basis for comparison 

 with Blechnum (Fig. 699). The fertile pinna has either one or two vascular 

 strands : the form of its transverse section is as in the simpler species of 

 Blechnnm: there is no obvious flange, but a curved wing on either side of 

 the mid-rib, which thins off at the margin (a). The concave surface is covered 

 over a very considerable area by sporangia together with glandular hairs. 

 The sporangia are not grouped in any definite sori, nor are there any 

 projecting receptacles (c). The origin of the sporangia appears to be almost 

 simultaneous, many appearing to be of like age in a given section {b). But 

 other sections show clear evidence of a mixed character, though the suc- 

 cession never seems to be long maintained. If a longitudinal section be cut 

 so as to traverse one of the wings vertically to its surface, the phalanx of 

 sporangia appears to be continuous (d). The veins severed transversely are 



