XLVI 



ELAPHOGLOSSUxM 



237 



The rhizome of E. latifolium (Sw.) J. Smith contains a stele nearly ap- 

 proaching the solenostelic state (Fig. 738, a), but with leaf-gaps sometimes 

 overlapping {b). The leaf-trace is much subdivided {c), and it is so from the 

 first, being given off as distinct strands {ci, b). Their arrangement suggests 

 comparison with a fully solenostelic type, such as Metaxya, but broken up 

 by perforations of the meristele at the leaf-base. As in Metaxya and 

 Lophosoria a. bud may be formed on the abaxial side of the leaf-base in 

 E. latifoliiun, its vascular suppl)- coming from the stele below the leaf-trace 

 itself {b, Fig. 738, b). 



The systematic arrangement of this large genus has been based on the 

 venation (Diels, I.e. p. 257), the steps of elaboration being similar to those 

 seen in Syngraiinne, and both being referable to a simple open venation as 

 in Metaxya: the latter is actually present in E. heliconiaefolia (Christ, I.e. 

 p. 133, Fig. ■j'i). But Elaphoglossmu shows advance on the other genera in 

 its dermal scales, which are often ver\- elaborate structures. 



Fig. 738. Elaphoglossiim latifolium (Sw.) J. .Sm. « = rhizome in transverse 

 section, showing only one leaf-gap. ^ = ditto, showing two leaf-gaps, X, Y, 

 while from the larger meristele the vascular supply is passing off to a bud [b). 

 t- = transverse section of the base of a petiole. ( x 4.) 



Such advances run parallel with the fully /\crostichoid soral state, the 

 whole lower surface of the young fertile blade being covered with a uniform 

 coating of sporangia, together with a few hairs. They arise from a deep 

 epithelium (Fig. 739, «): single cells grow out and enlarge {b, e), with the 

 usual three-sided segmentation and consequent three-rowed stalk: some- 

 times it appears only two-rowed at the base (d). The distribution of the 

 sporangia appears to be quite independent of the veins (e): later on by 

 interpolation of younger sporangia a "mixed" condition of the soral area is 

 attained. The spores have two flattened sides and a prickly surface, as 

 against the tetrahedral smooth spores of Syngranime and Metaxya. 



The conclusion suggested by the sum of these facts is that the three 

 genera form a series of which Metaxya is the most primitive, Syngranime 

 taking an intermediate place, while ElapJioglossnni is the most advanced. 

 They illustrate progress in the substitution of scales for hairs : in the sub- 

 division of the leaf-trace : in the increasing fusion of the veins of the blade, 

 while the latter is itself simplified in outline: in the extension and fusion 



