28 DAVALLIOID FERNS [CH. 



The genus as a whole is marked by great instability of leaf-outline. In 

 Diellia Mamiii Robinson, the leaf is diffusely bi-pinnate, with narrow 

 segments : it resembles that of Odontoso7na. From this state various steps of 

 condensation of the pinnae are illustrated, such as are shown by Diels 

 (E. and P. I, 4, Figs. 1 14). Sometimes various degrees of pinnation may be 

 seen in the same leaf: these lead through a reduced secondary pinnation 

 (Z?. alexandri Diels), and a simple pinnation with broad expanse (Z>, erecta 

 Brack., or D.falcata Brack.), to an almost cordate pinna {D. pinnila Brack.). 

 With this condensation goes an increasing anastomosis of the veins, ending 

 in a complicated network in the broadest. At the same time the sori recede 

 from the margin to the lower surface, and they tend to be linked into 



Fig- 597- Diellia fakata Hk. .-^ = a single pinna with coarse 

 reticulation, and sori intra-marginal, sometimes solitary on the 

 vein-endings, sometimes showing fusion to coenosori. B, C 

 show advanced examples of soral fusion. ( x 2.) 



coenosori, especially towards the base of the pinna. Such steps, illustrated 

 within the genus Diellia^ may be held as concomitants of condensation from 

 a type of leaf such as that of Odoniosoria. A like progression may be traced 

 homoplastically in other Marginal Ferns. 



The comparative conclusion from these facts is that Diellia originated from 

 some Davallioid type having diffusely branched leaves. It appears to be 

 related especially to Lindsaya and Odoniosoria, and in its insular isolation 

 to have carried out, independently of other related Ferns but homoplastically 

 with them, a progressive condensation of leaf-form and of soral fusion. This 

 genus, endemic in the Hawaiian Islands, where it is rapidly becoming rarer, 

 deserves a full comparative examination from this point of view before its 

 species become extinct. It would probably provide a convincing instance of 

 endemic variation, homoplastic with similar variation elsewhere. 



Odontosoria (Presl) Fee 



This is an old genus established by Presl in 1836, which comprises 

 19 species. Though included under Lindsaya in the Synopsis Filicum (p. 109), 

 and by Christ {I.e. p. 295), it is maintained as a substantive genus by Diels 

 {Nat. Pfianzenfam. 1, 4, p. 21 5). A wide synonomy indicates the close relation 



