Bower. — -Studies in the Phytogeny of the Filicales. 425 
beyond that point into this new marginal growth, just as they extend into 
the ‘ flange ’ in Blechnum. Prantl remarks (p. 44) that this is an indication 
how a dorsal position of the sorus may be held to arise from a terminal 
(marginal) position. The argument here corresponds closely to that in the 
case of Blechnum. It is true the bodies involved are different. But in both 
cases a thing which is originally marginal is shunted to the lower surface by 
strong unequal growth below it. In Mohria what has happened is more 
clear in the individual development than it is in Blechnum ; moreover, the 
final result is less marked than it is even in the section § Lomaria . But 
the condition of Eu-Blechnum is much more advanced still, for there not 
only is the ‘flange 5 very large when mature, but the original marginal 
growth of the leaf is continued directly into it, and the indusium and sorus 
appear as later structures, even originating from it. Here the transition 
from a marginal to a superficial position is complete, and finds no direct 
reflection in the ontogeny of its phyletic history. 
Biologically, such transitions appear to be most natural and intelligible. 
They secure for the young sporangia a better position in regard to protec- 
tion while young, and to dispersal of their spores when mature. And this 
being so, it is no matter for surprise that such changes should appear in 
more than one phylum of Ferns. But whereas in the Schizaeaceae it 
is seen in a typical representative of the Marginales ; in Blechnum , a repre- 
sentative of the Superficiales, the sorus was already upon the lower surface, 
and it is the indusial margin only which is shunted. 
(b) Modifications of the ‘ Fusion- sorus \ 
The disability of the strongly dimorphic type of Blechnum as regards 
nutrition may be obviated, as in the type of Eu-Blechnum , by the formation 
of the flange, and consequent enlargement of the assimilative area. But 
other methods are seen in other types, which are accompanied by modifica- 
tions of the fusion-sorus itself. These take the form of its disintegration 
and breaking up into separate portions. The methods of this, exemplified 
as an abnormality in Blechnum itself, and seen permanently in Woodwardia i 
Doodia , , S colop endrium^ and Asplenium, have been described in detail above, 
and may all be regarded as connected with enlargements of the assimilating 
area, with which the soral developments do not keep pace. The consequent 
breaking up of the fusion-sorus into parts may happen in different ways, 
which result in the characteristics of the well-known genera above named. 
Their various features are believed to be based on the following factors, 
which the study of the Ferns of Blechnoid origin have on analysis supplied : 
(1) Disintegration of the fusion-sorus, without any outward arching of 
the parts. This is seen abnormally in Blechnum itself, and becomes 
a regular character of the genera Woodwardia and Doodia ; also of Asplenium , 
usually with an oblique position and overlapping of the sori. 
