Bower —Studies in the Phylogeny of the Filicales . VI. 35 
that form of leaf. But is there any need for such a conclusion from the 
facts ? It seems more probable that both were differentiated from a common 
type, more nearly resembling the leaves of the less specialized Ferns. 
In systematic position he holds that Platycerium is not to be referred 
to Acrostichum ; nor is it near to Dip ter is or Cheiropleuria. He notes 
similarity to Nipkobolus , but considers that the prothallus points to the 
Cyatheaceae, and inclines to the view that it should form a special tribe 
linking the Polypodiaceae and Cyatheaceae. 
In the main this conclusion is in accord with my own view as expressed 
in Studies, No. V, excepting in the negation of the affinity with Cheiro- 
pleuria , and the erection of a special tribe. But as von Straszewski wrote 
without knowledge of the detailed facts which were there brought forward, 
he may revise his conclusion in view of them. Moreover, the additional 
observations on forms probably related, which are given above, will be helpful 
in placing this peculiar genus phyletically. It also is regarded as a Dipterid 
derivative, specialized for an epiphytic habit. The leaf-trace is subdivided, 
and the solenostele broken up by profuse perforation into a simple ring 
of meristeles in P. alcicorne , or with addition of medullary strands in 
P. stemaria. This arrangement finds its counterpart in the polycycle of 
the M atonia-Dipteris series. It is true this stat eseems far removed from 
the protostely of Cheiropleuria , but the difference is bridged over by the 
solenostely of Dipteris itself, and the profuse perforation now seen in 
Neocheiropteris and Leptochilus tricuspis. In view of the other similarities 
this obvious point of vascular difference must be discounted. 
It has been seen that in Dipteris each separate sorus is seated on the 
end of a blind intra-areolar vascular twig, which may be enlarged ; that in 
Cheiropletiria the enlarged vascular receptacle may extend in a lower plane 
beyond the limits of its own areola 1 : and that this extension carried 
to a greater extent gives rise to the well-known second vascular system 
of the fertile region of Plaiyceriuml This structure, which is here described 
as diplodesmic , is found also in Leptochilus tricuspis. It is significant that it 
appears in no other type of Acrostichoid Fern examined. The addition 
of this third example of a peculiar and rare structure, in a Fern less specialized 
than Platycerium, but showing in anatomy, in sporangium, and in spore- 
formation similarities to Platycerium , brings the latter into nearer relations 
to ordinary types, and tends to minimize its special peculiarities. On the 
other hand, the phyletic relation of the Dipterids to the Cyatheoids was 
probably a close one, both having sprung from a Gleicheniaceous source . 3 
This would sufficiently account for the character of the prothallial hairs 
noted by von Straszewski. Thus the additional facts accord with the 
reference of Platycerium as a Dipterid derivative. 
1 Ann. of Bot., vol. xxix, p. 512, Text-fig. 12. 
3 Studies, II, Ann. of Bot., 1912. Also V, 1 . c., 1915. 
2 l.c., p. 512. 
