CH. XXXVIl] 



DAVALLIA 



17 



are of comparative importance, suggesting for some of them a more primitive 

 position than that of Davallia itself For instance, in Davallia cojitigua 

 (Forst.) Spr. (G.-V., sHdes 951-952) there is an 

 almost perfect solenostele with occasional perfora- 

 tions, while each leaf-trace consists of two equal 

 strands. This is, however, one of the species in- 

 cluded in Prosaptia, and now referred to a position 

 elsewhere (see Chapter XLVIIl). Another excep- 

 tional type is Davallia dubia R. Br., which shows 

 a large solenostele, and an undivided petiolar 

 trace with incurved hooks (G.-V., slides 857-865). 

 The synonymy of this Fern is a sufficient indica- 

 tion of its doubtful position in Davallia, and its 

 probable Dicksonioid affinity. Putting such doubt- 

 ful cases aside, it may reasonably be held that 

 the vascular system of the typical Davallia is 

 really derivative from a solenostele with undivided 

 leaf-trace, as in Dennsiaedtia, with leaf-gaps 



overlapping alternately, and the meristeles be- Y\g. -,%<). Davallia disseda^.^^. 

 tween them attenuated. Each leaf-trace mean- Rhizome, slightly magnified. ^ = 



,.,.,.•11,.,, . rr vascular system dissected, and 



while IS divided to its base, coming off as a flattened to a single plane: = 



numberof separate strands; but referable in origin upper meristele; ?^=lower; /; = in- 



. * sertion of aleaf; a- = origin of alat- 



to the type of trace seen in Mtcrolepia {Davallia) eral shoot. ^= transverse section. 

 speluncae (L.) Moore (see Fig. 159, Vol. I, p. 166). (^^'^"^ Mettenius, from DeBary.) 

 According to the principles laid down in Vol. I, Chapters Vll-X, so highly 

 disintegrated a vascular system as that seen in Davallia indicates phyletic 

 advance, while this accords with the presence of dermal scales, not hairs, 

 covering the rhizome of true Davallias. Such a type as Davallia dubia, with 

 its solenostele and rusty hairs, will rightly take its place anatomically with 

 the Dennstaedtioid Ferns, where Sir W. Hooker placed it (5/. Fil. I, p. 71). 

 The general conclusion will be that by its scales in place of hairs, and by 

 its highly segregated vascular system, Davallia is a relatively advanced type. 

 The features of the sorus of Davallia also point towards phyletic advance. 

 Their appearance is shown in Fig. 588,/, K representing species both of 

 which fall under the section Eu-Davallia of Hooker {^Syn. Fil. p. 94). The 

 pocket-like sorus appears to be inserted upon the lower surface of the pinnule, 

 but comparison with the Dennstaedtiinae and with other related Ferns 

 suggests its derivation from a two-lipped sorus of the Dicksonioid type, by 

 progressive inequality of the upper and lower indusia: the former becomes 

 incorporated with the general leaf-surface, as in Hypolepis, the latter fusing 

 at its margins with the expanse on which it is borne, and forming the closed 

 and sometimes deeply protective pocket characteristic of the genus. The flat 



