Bower.—Studies in the Phytogeny of the Filicales. 527 
can be at present no more than a suggestion of a possible relation of other 
living Ferns to the group under consideration. 
It would thus appear that we may have in some measure to revise the 
current view of the Matonioid-Dipterid phylum. They are commonly held 
to have been a series of Gleichenioid origin, which was prevalent in the 
Mesozoic Period, but struggled on to the present time only in the surviving 
genera Matonia and Dipteris. There can now be little doubt that Cheiro- 
pleuria must be added to these surviving types, while Platycerium can hardly 
be anything else than a highly specialized Dipterid, related especially to 
Cheiropleuria , and adapted to modern life under the peculiar conditions 
of epiphytism. And it is possible that other derivative forms may be 
ultimately added to those modern representatives of a very ancient sequence. 
Finally, if the position ascribed be accepted, the case of Cheiropleuria 
will have its value in showing that, in special cases, a want of parallelism of 
the several criteria is to be recognized and even expected. Many cases are 
already known. For instance, the single initial cells in stem and root of the 
Eu-sporangiate Ophioglossaceae, and the massive dermal appendages on 
the leaf-base of the primitive Gleichenias ; the reticulate venation of the 
Eu-sporangiate Kaulfussia ; the high subdivision of the vascular tracts in 
the living Marattiaceae; the protostelic structure combined with advanced 
gradate sori of the Hymenophyllaceae. But such instances of the absence 
of parallelism in the several criteria are relatively slight compared with the 
glaring fact of the primitive protostely, and simple hairs accompanying 
in Cheiropleuria a mixed sorus of an advanced ‘ Acrostichoid ’ type. It is 
this strange collocation of characters, which comparison marks out as 
incompatible elsewhere, that gives to Cheiropleuria its special interest and 
value in relation to the phyletic study of the Filicales. 
Summary. 
t . Cheiropleuria bicuspis (Bl.), Presl, is the only known species of 
a substantive genus. 
2. It shows an uncommon mixture of primitive and advanced characters, 
by which it takes a place phyletically as a synthetic form. 
3. Its characters, external and internal, connect it downwards most 
clearly with Dipteris ; and upwards, that is in the direction of more advanced 
specialization, with Platycerium . 
4. Its simple hairy investment, protostelic axis, undivided leaf-trace, 
and its frequently bifurcate form of leaf, are relatively primitive characters. 
5. Its reticulate venation and its ‘ Acrostichoid ’ and ‘ mixed ’ sorus are 
characters of relative advance* 
6. The occasional extension of the receptacular vascular supply of the 
individual sorus beyond the single vascular areola gives the clue to the 
