Bower.—Studies in the Phytogeny of the Filicales. VII. 55 
the lower indusium reduced and abortive; the upper flattened out, and 
assimilated to the laminar surface, while it is traversed by a vascular strand 
extended from the receptacle. But it is not phyletically a lobe of the 
lamina, however nearly it may resemble one. It is originally a superficial 
indusial growth, as in the Dicksonioid Ferns. All of the Ferns involved in 
this series are rhizomatous and solenostelic, with united leaf-trace ; bearing 
hairs, not scales; and they have highly ramified leaves, with open venation. 
A 'Polypodium' type is thus seen to arise by modification of a Dicksonioid 
type. It is, however, to be noted that if the phylesis here suggested is 
correct, Polypodium punctatum will have no relation by descent with 
Phegopteris or Dryopteris , which names have been applied to non-indusioid 
Nephrodioid Ferns. The absence of scales and the solenostelic structure of 
Fig. 41. a. Sorus of Acrophorus nodosns in surface view. ( x 35.) b. Pinnule of the same, 
showing the vein continued beyond the sorus. ( x 10.) 
our series is in strong antithesis to the scaly habit and advanced dictyostely 
of Phegopteris and Dryopteris. The phyletic distinctness of the Dicksonioid 
and Cyatheoid series has been indicated elsewhere, 1 the one having con¬ 
stantly marginal and the other as constantly superficial sori. Thus the 
sources from which Polypodium punctatum and Phegopteris are derived are 
themselves distinct. 
On similar grounds it would seem probable that Acrophorus nodosus 
finds its proper place with the Nephrodioid Ferns. Its sorus is seated 
sometimes on the enlarged apex of a vein, as its name implies (Fig. 41, a), 
but frequently it may appear laterally on a vein (Fig. 41, b): and the 
difference may be seen illustrated by sori on the same leaf. The indusium. 
which corresponds in position to that of Nephrodium —or indeed to that of 
the vestigial inner indusium of Polypodium punctatum —is often so small that 
1 Studies, III. Ann. of Bot., vol. xxvii, p. 471. 
