Bower . — Studies in the Phytogeny of the Filicales. 397 
usual pinnate venation to the tip. The best understanding of the rather 
complex ‘ Acrostichoid ’ soral condition is obtained by examining first the 
apical region of a pinna (PL XXIX, Fig. 18). The distal veins may be sterile, 
but soon small groups of sporangia appear, forming isolated circular sori at 
points at, or outwards from, their bifurcation. Further down the venation is 
connected by vascular commissures forming arches, which finally become 
continuous, and serve as a basis for a connected soral line on either side of 
the midrib. Further back from the apex, the soral bands may extend out- 
wards along the veins, so as to constitute broad, apparently ‘ Acrostichoid ’ 
tracts. If a transverse section be cut through such a pinna in the young 
state it will appear as in Text-fig. 13, B ; and a comparison with a similar 
section of Woodwardia (Text-fig. 13, w) shows the remarkable similarity 
which may exist. The outline and vascular 
arrangements are the same ; the difference 
lies in the absence of the indusium in 
Brainea. 
The details of development of the fertile 
pinna have their bearing on the relation of 
this Fern to the Blechnoids. The wing of 
the pinna shows as usual the marginal cell with 
alternate segmentation (PL XXIX, Fig. 19,^). 
Very soon, cells project upon the lower sur- 
face, forming a rounded upgrowth, upon which 
young sporangia may soon be recognized 
(Fig. 19, b). This corresponds in position 
and in office to the sorus of Blechnum or 
Woodwardia , but differs in the entire ab- 
sence of the indusial flap. It had been 
anticipated that possibly vestigial indications of an indusium might be 
seen in Brainea , which would confirm the comparison ; but none have been 
found. At first the succession of the sporangia is basipetal, those in the 
centre of the upgrowth being most advanced (Fig. 19, a); but this is not 
usually maintained, and younger sporangia are found between those more 
advanced, showing thus a progression towards a ‘ mixed ’ condition of 
the sorus (Fig. 19, b } c). Moreover, the locality of the sorus is not 
restricted to the commissure close to the midrib, but is liable to spread 
towards the margin, following especially the outward course of the veins 
(Fig. 19, c). Using these facts according to the usual comparative 
method, the following conclusion may be drawn : That Brainea is a type 
sprung from a gradate ancestry with restricted sorus, and that it has 
progressed to a mixed condition, and has lost the strict limits of its soral 
area, the sporangia having spread outwards, and assumed an ‘ Acrostichoid * 
character. The type from which it arose — as indicated by the soral 
E e ? 
Text-fig. 13. w, transverse sec- 
tion of the midrib and sori of Wood- 
wardia radicans (L.), Sm., showing 
the indusial flaps. B, a similar section 
of the pinna of Brainea insignis (Hk.), 
J. Sm., showing the same relations, but 
with the absence of an indusium. x 35. 
