618 FILICALES 



a careful revision, with special reference to their anatomical characters, 

 before this progression can be regarded as established. 



MATONIA-DIPTERIS SERIES. 



The genus Dipteris, Reinvv., so long merged in the comprehensive genus 

 Polypodium on account of its sorus being naked and superficial, has recently 

 been restored to its independent position, and is now held to be the sole 

 representative of the family of the Dipteridinae. 1 There is little doubt 

 that this position is justified, while among relatively primitive types the 

 family finds near allies among the Matonineae. 



The genus is represented by four living species from the Indo- Malayan 

 Flora, which illustrate an interesting progression in leaf-architecture. They 

 all have creeping rhizomes, showing occasional dichotomy, the type of shoot 

 being closely similar to that of Matonia. The axis and the bases of the 

 leaves alike are invested with a dense covering of hairs, which are, however, 

 flattened into elongated scales, an advance upon the filamentous hairs of 

 Matonia. The leaves of the different species vary in area, but are alike 

 in plan : upon the end of a long petiole is borne a lamina which is repeatedly 

 branched in a dichotomous manner. The branches may remain narrow, with 

 a marked midrib and lateral flanges of no great area, as in D. Lobbiana, 

 Hooker, and D. quinquefurcata, Baker : or they may be broader, and be 

 more or less webbed into a lamina, which is, however, still divided by a 

 median sinus into two symmetrical halves : this is seen in D. conjugata, 

 Reinward (Fig. 343 A), and D, Wallichii, Hook, and Grev. This leaf- 

 structure is comparable with that of Matonia, in which also the outline of the 

 lamina is referable to a dichotomous branching, and as in that genus, so 

 here also the sori are in the narrow-lobed species disposed upon the flanged 

 wings on either side of the midrib. Their relation to the area of the leaf- 

 surfaces within this very natural genus is instructive for comparison with 

 other Ferns. In the narrow-leaved D. Lobbiana, and especially near to 

 the bases of the several lobes, the sori form a regular linear series on 

 either side of the midrib (Figs. 344 and 343 E). In D. quinquefurcata the 

 lamina is larger and the segments broader than in D. Lobbiana, and the 

 areolae within the veins on either side of the midrib are larger, and contain 

 more sori : these illustrate various degrees of fission, and thus they become 

 spread over the enlarging area (Fig. 345). D. Wallichii appears to occupy 

 .a middle position between these species and the large D. conjugata ; for 

 it is described as having the ultimate segments linear in form, and the 

 sori as being similar to those of D. conjugata, but more numerous than 

 in D. Lobbiana or quinquefurcata. Lastly, in the large-leaved D. conjugata 

 the bifurcate lamina is broadly webbed, and the very numerous small 

 sori, which are distributed over the wide expanse, may be circular or oval, 

 .and not always distinct from one another: they may vary much both in 



1 Seward and Dale, Phil. Trans., vol. cxciv., p. 487. 



