Filicales. 
249 
record of that genus certainly bears out Professor Bower’s view 
that this obliquity is primitive. 
The Cyatheaceae and Polypodiaceae do not appear to approach 
the Botryopterideae at all closely, but we shall see later that there 
may possibly be a connection through the Gleicheniaceae between 
the Cyatheaceae and Polypodiaceae and certain Primofilicinean 
ancestors of the Botryopterideae. 
To the Hymenophyllaceae, the Cyatheaceae and Polypodiaceae 
show hardly any points of resemblance, except those characteristic 
of the Ferns generally. The basipetal succession of the sporangia 
in the filmy ferns, and some Cyatheaceae and Polypodiaceae, is 
probably due to parallel development. It is fair to add that Diels 
suggests a rather close affinity between the Hymenophyllaceae and 
Polypodiaceae, but he adduces no fresh evidence in support of this 
idea (14). While we cannot look upon the Schizaeaceae as the 
ancestors of the Cyatheaceae and Polypodiaceae we may expect 
a close affinity to the Gleicheniaceae. 
Some structure resembling the “ nodal island” of Gleichenia was 
probably the precursor of the dorsal phloem-strand of the Lindsaya- 
stele. The C-shaped trace of the Gleicheniaceae is frequently found 
in the anatomically simpler Cyatheaceae and Polypodiaceae, while 
the numerous varieties of traces in the‘more complex forms are all 
referable to more or less profound modifications of this original 
C-shaped type. Though the fronds of the Cyatheaceae and 
Polypodiaceae are usually pinnately divided, the relatively ancient 
genus Dipteris has retained a form of dichotomy. Further, the 
sporangia of all three orders are soral. In Gleichenia the sporangia 
usually form a single series (as do those of some species of Dipteris), 
but in G. dichotoma there are supernumerary sporangia (7) and 
these, though they arise simultaneously with the others, foreshadow 
the elongation of the receptacle on which the sporangia of the 
Cyatheaceae and simpler Polypodiaceae occur in basipetal succession. 
Professor Bower has also established the homology of the annulus 
in these orders (7). On the whole, then, the similarities enumerated 
above seem to indicate that it is among the most primitive 
Gleicheniaceae, now extinct, that we must look for the ancestors of 
the Polypodiaceae and Tree Ferns. But since the stele of Loxsoma 
is exarch and since this genus, from its similarity to these orders, 
presumably had a relatively recent common origin with them, and 
since its exarchy appears, on general grounds, to be primitive, it is 
likely that the Gleicheniaceous ancestor of the Cyatheaceae and 
