526 B outer.—Studies in the Phytogeny of the Filicales. 
But in respect of the venation in the fertile region of the sporophyll, 
Cheiropleuria is in closer relation to Platycerium. It has been shown above 
how the receptacular strand in Cheiropleuria may pass, in a lower plane, 
out of its own vascular areola, thus initiating an independent course of its 
own. The same may be found in Platycerium , though here it is on a larger 
scale ; and it leads to the formation of that second vascular system described 
by Mettenius, which spreads in a lower plane, between the main system of 
the leaf and the sori themselves. This condition is so exceptional among 
Ferns that the degree of correspondence demonstrated between Cheiro¬ 
pleuria and Platycerium , in this respect, gains thereby additional weight. 
It may therefore be held that the points of similarity seen in their leaves go 
far to outweigh the differences of stelar structure in the stem between these 
two genera. 
In its dermal appendages—whether the flattened scales of its rhizome, 
or the stellate hairs which cover the young sori— Platycerium shows an 
advanced condition. But the sorus itself, though the receptacles are greatly 
elongated, are still not typically ‘ Acrostichoid as in Cheiropleuria ; each, 
though prolonged, maintains its individuality, while the sporangia originate 
almost simultaneously. The sporangia themselves have the usual three- 
rowed stalk, and the annulus is more definitely interrupted than in Dipteris 
or Cheiropleuria. Thus sorally Platycerium shows a curious mixture of 
characters, some in advance of those of Cheiropleuria , others, and especially 
the distinctness of the sori, being more primitive. 
The sum of the features noted in the above paragraphs appears to 
place Platycerium definitely in phyletic relation to the Matonia-Dipteris 
Series, as a form probably derived from such types, but curiously specialized; 
and perhaps its high degree of specialization to an epiphytic habit may 
account for the strange mixture of its characters. The anatomy of its 
stem relates it rather to Matonia and Dipteris ; but its leaf, and its soral 
state points to Cheiropleuria. It may probably be held not to have been 
actually derived from any one of the living genera, but rather as a curiously 
specialized form, sprung from some extinct Matonioid or Dipterid which 
had a relatively advanced vascular structure; and that the soral system 
became specially enlarged, thereby giving a high spore-output, advantageous 
as an offset to the difficulties of an epiphytic habit. 
The question remains whether any other Matonioid-Dipterid deriva¬ 
tives may be recognized among living genera. This question cannot be 
answered satisfactorily without much further comparative study. But it 
seems probable that others may actually be related. For instance, Lepto - 
chilus tricuspis was placed close to Cheiropleuria by Sir W. Hooker, 
Neocheiropteris also is probably related, as well as some others ranked 
at present as species of ‘ Polypodium ’. A careful comparative study of 
such types, upon which I have already entered, would go far to decide what 
