“anit 
DENNSTAEDTIA-DAVALLIA SERIES \« 615 
uniformity of structure of the sorus on the mixed plan, with flat receptacle, 
and with no definite rule of orientation of the long-stalked sporangia. 
The connection of the Dennstaedtia-Davallia series 
-with such genera as Lindsaya, Pteris, Pellaea, and 
Adiantum, where the sori are marginal, seems beyond 
question, and it is strongly supported by the anatomical 
evidence. But, on the other hand, the sori are liable 
to move from the marginal position: this phyletic 
change is illustrated by very gradual steps. An 
inequality of the lips of the indusium is apparent in 
Microlepia (Fig. 332 a): it appears often in greater 
degree in the various forms of Davadlia, and is 
specially marked in § Leucostegia (Fig. 340), where 
the upper lip appears as the continuation of the leaf- 
lobe, the lower as a cup-shaped indusium apparently 
some distance from the margin. Lezcostegia has long 
been recognised as closely related to Cystopterts, which 
also has a mixed sorus, without regular orientation 
of its sporangia, while it is protected by an indusium 
Fic. 340. 
Davallia hymenophyll- 
oides. Pinnule enlarged. 
(After Hooker, from Christ’s 
Farrnkraiiter.) 
of similar form to that of Zeucostegia (Fig. 341). These examples will 
serve as illustrating a feature which has probably been widely effective 
Fic. 341. 
Cystopteris fragilis. Pinnule of the form from 
‘Tasmania, and its sorus enlarged. 
from Christ’s Farrnkrduter.) 
(After Hooker, 
in the descent of the Leptosporangiate 
Ferns, viz. the retreat of the sorus from 
the margin to the under surface of the 
leaf. From Cystopteris the sequence 
may with probability be traced on to 
the Aspideae. It would thus appear 
that a considerable proportion of the 
Mixtae are referable in origin to forms 
with a marginal position of the sorus. 
A further illustration of probable 
relationship, in this case to olypo- 
dium, is seen in Hyfolepis. This 
genus was included by Kiihn and by 
Prantl! in the Dennstaedtiinae, though 
by others it has been placed in the 
Pterideae. The marginal sori, covered 
by the reflexed margin of the leaf, 
consist of a slightly convex receptacle, 
upon which the sporangia of various 
ages are inserted in no definite order: 
the annulus is definitely interrupted 
at the insertion of the stalk. It is clearly one of the Mixtae, but the 
affinity with the Dennstaedtiinae is indicated by the position and character 
Z Lute, p. 18. 
