Bower . — Studies in the Phytogeny of the Filicales . 409 
species of Blechnum of a rather advanced type. If sections be cut of a pinna 
not strongly divergent from the normal Blechnum arrangement of sorus, the 
structural correspondence is very close with such a species as B. spicant. 
Fig. 29 ,g, shows this ; there is a considerable flange, with the sorus distinctly 
intramarginal in origin. The indusial flap is rather late in its development, 
while the sporangia may show in their early stages distinct traces of a basi- 
petal sequence. This is not, however, maintained. 
But if sections be examined which traverse a diverticulum of the fusion- 
sorus, so that the two sides of the curve be cut through, the appearance 
presented is as in Fig. 29, /, h . The former represents a very early state, 
in which a deep depression of the surface indicates where the soral develop- 
ment is to take place, while right and left procambial strands mark the 
position of the vascular supply. The points of greatest convexity which lie 
above these show by wedge-shaped superficial cells the places of origin of 
the opposed indusial flaps. Fig. 29, h, shows a more advanced state, though 
the deep depression remains as in the younger state. The slight convexities 
right and left have grown out into indusial flaps, consisting at their bases of 
two layers of cells, but thinning to a single layer at their margins. Beneath 
them are the vascular strands corresponding to the commissures of Blechnum ; 
seated on them are the sori, the sporangia showing again some indication of 
a basipetal sequence. The whole structure is plainly a duplication of a single 
fusion- sorus of Blechnum , with the two receptacles face to face, as they would 
be in consequence of the sinuous curving of the ordinary fusion-sorus. 
The conclusion which follows is then this. That in the var. Krebsii we 
see a Blechnoid Fern which has widened its fertile pinna beyond the normal ; 
that this widening is accompanied by a sinuous curving, and often also by 
disruption of the fusion-sorus and by extra branchings of the veins ; beneath 
all this there may be recognized, by the characters of the venation and the 
margin sinuosities, an imperfectly developed secondary pinnation, such as is 
actually seen to exist in B. Fraseri and in Sadleria. 
Scolopendrium. 
But B. punctulatum, war. Krebsii, was originally described by Kunze as 
Scolopendrium Krebsii . This raises the question of the relation of Scolo- 
pendrium to Blechnum. It is best to approach it through a comparatively 
simple and regular species, such as .S', vulgare , L. The relation of the sori 
to the venation in this Fern and to the sinuosities of the margin is shown in 
PL XXXI, Fig. 30. It is seen that the primary veins arising from the midrib 
bifurcate twice, or sometimes more. On the outermost branches of each 
group, and facing outwards from the centre of the branch system of each 
primary vein, are the well-known elongated sori. As the sori connected 
with the successive primary veins face one another, the consequence is 
the arrangement typical of Scolopendrium (see E. u. P., i. 4, Fig. 123, b). 
