3 1 8 Bower . — Studies in the Phytogeny of the Fi lie ales, 
two of the pairs of genera discussed above, viz. Struthiopteris and Onoclea 
— Peranema and Diacalpe — Woodsia and Hypoderris — Cystopteris and 
Acrophorus — were related in the sense of being successive steps in a simple 
phyletic line. That is to say, no one of these groups can be held as 
the actual ancestors of another. It has been remarked above that none of 
these Ferns is really primitive. All show indications of a middle position 
in the general scale of the Filicales. The source from which they spread 
has without doubt been related to that of the Cyatheaceae, as shown by 
habit, by anatomy, by sorus, and in some cases by the details of the 
gametophyte. But in view of the anatomical and soral characters combined, 
it is difficult to relate any of them to any definite genus of the Cyatheaceae 
as we see them now. These Ferns with basal sori appear collectively to 
form a brush of separate minor lines of descent, related one to another by 
common origin, but separately specialized according to their habitat. The 
Cyatheaceae are essentially the intertropical forest representatives, showing 
increasing specialization in soral protection, in accordance with their den- 
droid habit. Struthiopteris and Onoclea are forms with still more special 
protection of the sori by incurving leaf-margins, in relation to their 
northern and mountain habitat. Similar circumstances have probably 
influenced Peranema and Diacalpe , and led to specialization of their sori 
along a distinct line of their own. Woodsia is a boreal dwarf type, and 
Hypoderris a type of tropical shade. Cystopteris is a world-wide type, but 
with its head-quarters in the temperate zones of both hemispheres. It 
is specially marked by its hardihood and resistance to alpine extremes. 
Most of the smaller genera are deciduous according to season, a character 
clearly indicating their specialization for life under marked seasonal change. 
This is in contrast to their larger and more successful correlatives, the 
intertropical Cyatheaceae, which maintain their constant tuft of leaves. 
The Cyatheaceae are clearly the most successful, as measured by size, 
as well as by number of species. They were probably also the earliest 
type. The smaller genera show by their paucity of species, and in some 
cases by their limited spread, that they have met their external circum- 
stances with only partial success. But indirectly in relation to two of them 
great phyletic developments have probably arisen. In near connexion with 
Cystopteris (and probably also in some relation with Peranema and Diacalpe ), 
the great sequence of the Aspidieae has come into existence. Similarly, 
in relation to Struthiopteris has arisen the successful sequence of Lomaria, 
Woodwardia , and Doodya, Here it must suffice merely to suggest these 
lines of further progress, and the full discussion of them must be left over 
for a future occasion. The object here is to indicate that the Cyatheoid 
type, with gradate sorus and basal indusium, was not a blind or final 
evolutionary line, though very likely the genera of Cyatheaceae, as we see 
them to-day, were the ultimate exponents of it. Modifications, and espe- 
