384 Bower. — Studies in the Phytogeny of the Filicales. 
the median line, so that, as the segment has here enlarged to form the 
midrib, the new growth inclining towards it covers in the concave lower 
surface. The part of this surface directly overarched becomes the recep- 
tacle, which is here flattened. Vascular tissue, constituting a strand on 
either side of the midrib, has meanwhile been formed internally at a point 
slightly nearer to the midrib than the receptacle itself (Fig. 13, e,f). This 
is the commissure usual in the genus, and from it a vascular extension may 
be continued towards the margin of the flange. The latter has meanwhile 
enlarged, its tissues become lacunar, and it may bear stomata (Fig. 13,/). 
The sporangia are produced upon the flat receptacle in close order, and 
almost simultaneously, but traces of a basipetal sequence are evident, as 
indicated by the various stages of segmentation which may be seen side by 
side. For instance, in Fig. 13, e, the middle sporangium of the five shown 
is slightly in advance of the others. This basipetal sequence, slight though 
it is, appears to be maintained with a high degree of constancy, though 
occasional departures from it have been observed, but there is no confirmed 
condition typical of the Mixtae. The area over which the sporangia are 
spread is worthy of note. They may extend beyond the flange on to the 
‘ indusial * margin. This may be held as an indication of its foliar nature, and 
that it is not a mere indusium such as is seen in certain other types of Ferns. 
The petioles of B. Fraseri are thinner than in other species, and show 
the usual two-hooked adaxial strands, and between them one or two smaller 
strands constituting a relatively simple horseshoe. 
(K) B. ( Salpichlaena ) voltibile , Klf. 
This tropical American species is, like B. Fraseri , bipinnate, but differs 
from it greatly in size, and in having adopted a climbing habit somewhat 
like Lygodium. A good representation of it is given in Hooker’s Garden 
Ferns, Plate XV. The leaves are not dimorphic as a rule. The pinnules are 
very large, with ‘ the fructification of a Blechnum i. e. sori parallel to and 
closely adjoining the midrib, and with a very wide expanse of assimilating 
‘ flange ’. No material has been available for developmental study, but the 
mature structure leaves no room for doubt that the development would 
prove to be of the ordinary Blechnoid type. 
Hooker, in his Garden Ferns, points out the ‘ very close resemblance 
to our Lomaria volubilis\ The difference lies in the latter being dimorphic, 
with narrow fertile pinnules. But the detailed drawing in the Species 
Filicum, vol. iii, PI. CL, Fig. 3, clearly shows the presence of a rudimentary 
flange. We have seen in certain species of Blechnum how variable the 
development of the flange may be, especially in B. gibbum , so that there 
can be no definite line drawn between the Blechnoid and the Lomarioid 
states. This fully justifies the merging together of the two Ferns named 
as forms or varieties of the species B. volubile , Klf., which has been done by 
