2i8 GLEICHENIACEAE [CH. 



Mertensia, and covering the same species excepting as mentioned below: 

 (ii) Eu-Gleichenia in the sense of the Synopsis Filiaun: and (iii) E21- 

 Dicranopteris, under which name I propose to rank those two outstanding 

 species, known as G.pectinata (VVilld.) Pr., and G. linearis (Burm.) Clarke, the 

 latter including G. nervosa (Klf.) Spr. Syst., which is held to be a variety of 

 G. linearis in the Synopsis Filiciim. Hooker had already separated these 

 species from the rest of the genus, each in a distinct section, but without 

 any special designation. They have in common the presence of hairs, not of 

 scales as in the other two sections: the sorus has its centre not vacant as in 

 other Gleicheniaceae, but occupied by one or more sporangia. Moreover, G. 

 pectinata has solenostelic structure. These characters sufficiently distinguish 

 this section from the other two. 



As regards the phyletic relations of the genera and sub-genera thus 

 distinguished, a central position is to be accorded to the sub-genus Dicran- 

 opteris, and particularly as represented by such a species as G. flabellata, on 

 the ground of the Pecopterid-type of the leaves, with flat pinnules, and of 

 the consistently protostelic structure of the axis: of the numerous uniseriate 

 sori, with 4-6 sporangia, having relatively large spore-output from each, 

 and sometimes with large antheridia and numerous spermatocytes. These 

 features are all held to be relatively primitive, but they may be associated 

 with scaly ramenta, and contracted petiolar meristeles, which are features 

 of relative advance. 



The sub-genus Eu-Gleichenia is held to comprise xerophytic derivatives 

 from the central type, as shown by the contracted and often concave pin- 

 nules, usually with only a single sorus of very few sporangia, each having 

 a relatively low spore- output. Ramenta are present. The same may be said of 

 Stromatopteris, which is also regarded as a specialised xerophyte, its under- 

 ground rhizome being an important feature in its success. The spore-output 

 per sporangium is, however, larger than in Eu-Gleichenia, and the dermal 

 appendages are very variable, including ramenta. 



Platyzoma is also a highly modified xerophyte, as shown by the prevalence 

 of sclerenchyma in the rhizome which has signs of advance towards soleno- 

 stely, and is densely covered with hairs. The exiguous leaves resembling those 

 of the Eu-Gleichcnia-\.y\iQ and its isolated sori confirm this. The spore-output 

 is the smallest in the Family, and it goes along with the peculiar heterospory. 

 Thus Eu-Gleichenia, Stromatopteris, and Platyzoina may all be regarded as 

 xerophytic derivatives from a type like Dicranopteris. 



It will not be possible to arrange the Family in a simple linear sequence, 

 so as to show correctly the phyletic relations of the genera and sub-genera. 

 It must therefore suffice to enumerate them in catalogue form, giving in 

 a few words the substance of the foregoing comparisons. Gleichcnia itself 

 undoubtedly holds a central position, and the genus is sub-divided thus : 



