314 Bower* — Studies in the Phytogeny of the Fi lie ales. 
a spore-output of approximately 6 4. Alsophila has a definitely dendroid 
habit. The protostelic and solenostelic stages are quickly passed over 
in the young axis, and a dictyostelic structure is adopted, with internal 
accessory bundles. Superficially it bears broad scales as well as hairs, and 
the former at the leaf-bases are, as in G. pectinata, borne on peg-like 
emergences. These characters collectively indicate for Alsophila a state of 
advance upon what is seen in Lophosoria. 
Hemitelia shares in the main the anatomical and soral characters 
of Alsophila , but its distinguishing feature is the ‘ indusium ’. Christ (‘ Farn- 
krauter’, p. 329) describes the genus appositely as a small one, ‘which as 
regards the indusium is midway between Cyathea and Alsophila , since the 
sorus is in fact naked above, but is provided at the base with a scale-like 
rudimentary indusium \ This indusium is described as variable in size by 
various writers. In form and structure it is very similar to the scales found 
on the surface of stem and leaf, and the probable view which follows from 
this fact is that it simply represents one of these scales turned to a special 
protective use. 
In Cyathea the most specialized type of the series is seen, with lofty 
dendroid habit, complex structure of the axis, profuse covering of the 
surface of axis and leaf with chaffy scales. The sori are gradate, and are 
protected and sometimes completely covered in by the basal, cup-like 
indusium. This is clearly comparable with that of Hemitelia , but it has 
lost its scale-like character, and is usually developed equally all round the 
sorus. The sporangia are of the same type as in the other genera, but 
in C. dealbata they are of specially small size, and show a spore-output 
reduced to the unusually low figures of 1 6, or even 8. These characters 
collectively indicate that Cyathea is the most specialized genus of the whole 
series. 
When the parallelism of the external, the anatomical, and the soral 
facts for the sequence of Ferns thus laid out is fully taken into account, 
it seems impossible to doubt that in essentials it illustrates a true phyletic 
progression which has taken place. It is not asserted that any modern 
Gleichenia was the progenitor of Lophosoria or of any other Cyatheoid 
Fern. Probably the Gleichenias as we know them are a blind branch. 
What is concluded is that from an essentially Gleichenioid type long ago 
the Cyatheoid type of Ferns originated, and an essential link in the pro- 
gression is supplied by Lophosoria . The progression involves a gradual 
change of habit from a creeping type with isolated leaves borne by an 
elongated rhizome, to an erect type which includes the largest of the Tree- 
Ferns. It necessarily follows that here at least the upright axis is a 
secondary result of evolution. A similar comparison applied among the 
members of the quite distinct sequence of the Dicksonieae leads to a like 
result; this will be taken up in detail on a subsequent occasion. From 
