OO Gn, Se a CNN. 
HOOKER LECTURE, 1917. 119 
Vaughan, and Lang. These have filled in many of the links in the chain 
of evidence. They tend to demonstrate a consistent progression in stelar 
structure of the primitive Ferns, fossil and living. It is found to accord 
generally with the characters of their fructification, and with stratigraphical 
sequence. It is true that on purely anatomical grounds, and without due 
reference to the phyletie position of the Ferns compared, or the cogency 
of their stratigraphical sequence, objection had been taken by the Harvard 
School to certain well-founded conclusions. But this serves mainly as 
a warning against reasoning based, as theirs has been, upon a single line 
of evidence, pursued without due consideration of others. 
The second method of investigation is by the enquiry into those Ferns 
which bear many synonyms, and have obviously been difficult of classi- 
fication under less searching methods. They now stand revealed as missing 
links in the phyletic chain. Their being such explains the difficulty they 
had presented to the early Systematists. As examples, Lophosoria, Metarya, 
and Cheiropleuria may be quoted. Each of them had been merged by 
Sir William Hooker, in consequence of his aversion to anatomical evidence, 
into other large comprehensive genera. But they have since been re- 
established as substantive genera. Lophosoria links the Gleicheniaces with 
the Cyatheæ ; Metaxya helps to connect the Gleicheniacee with Elapho- 
glossum ; while Cheiropleuria indicates how, from a type like the Dipterids, 
a number of later forms may have sprung—and in particular that strange 
genus, Platycerium. Another most important connecting type is Lowsoma, 
and probably also the little-known Costa-Rican Fern, Loxsomopsis, which 
indicate a transition from the Schizæaceæ to the Dicksonioid Ferns. But 
we need not here attempt to exhaust the list of such connecting types. It 
is merely intended to indicate how their recognition serves to link up those 
sequences which form the lower branches of a phyletic system of the 
Filicales. 
An intensive study of large genera is another line which has been pursued 
with success. For instance, the examination of many species of Blechnum 
has disclosed how that genus, springing from some Matteuccioid source, 
formed its characteristic fusion-sorus. This then spread over the leaf- 
surface to form the Acrostichoid developments of Brainea and Stenochlena : 
or it broke up into short lengths, as in Woodwardia and Doodya ; or, if 
these were displaced by surface-growth, the result appears in the cha- 
racteristic features of Scolopendrium and Asplenium. These are quoted 
as instances of the methods now being pursued in the phylesis of Ferns, 
and of the results which have followed. 
A consequence of the more firm establishment of a number of distinct 
phyletic lines has been to show more distinctly than before the falseness of 
certain old-established genera, practically convenient as these may have been. 
Polypodium, Acrostichum, and Gymnogramme, in the old comprehensive 
sense, are all doomed to dissolution, They are not genera in the phyletic 
