Bower . — Studies in the Phylogeny of the Filicales. 393 
strands, usually about four to six, forming a horseshoe of a relatively 
advanced type, as compared with such species as B. filiforme and alpinum. 
The development of the fertile pinna has been only imperfectly traced 
owing to the youngest stages not having been obtained. But sufficient has 
been made out to give a basis for comparison with those species of Blechnum 
which approach Stenochlaena in other respects. The fertile pinna has 
either one or two vascular strands in the midrib, or sometimes even a third 
may be present between the two larger ones. The form of the transverse 
section is apparently as in the simpler species of Blechnum , such as 
B. lanceolatum ; there is no obvious flange, but a curved wing on either side 
of the midrib, which thins off at the margin, but not as a rule to a single layer 
of cells (Plate XXVIII, Fig. 17, a). The concave surface of this is covered 
over a very considerable area by hairs with glandular heads of the Blechnum 
type, and sporangia ; the latter are not grouped in any definite sori, nor are 
a. 
b. 
Text-fig. ii. Stenochlaena sorbifolia (L.), J. Sm. Transverse sections of the stock ; 
a and b show different sizes and complexities of construction, x 4. 
there any projecting receptacles (Fig. 17, c). The origin of the sporangia 
sometimes appears to be almost simultaneous, many appearing in a given 
section to be of like age (Fig. 17, b). But other sections show clear evidence 
of a 6 mixed ’ character, though the succession never seems to be long main- 
tained. If a longitudinal section be cut so as to traverse one of the wings 
vertically to its surfaces, the phalanx of sporangia appears to be continuous 
(Fig. 17, d). The veins severed transversely are widely apart, and quite 
distinct from one another ; there is in fact no vascular commissure present, 
linking the veins together as is usual in Blechnum. It is seen that sporangia 
arise from the whole leaf-surface intervening between them. The condition 
is distinctly c Acrostichoid and there is no isolation of distinct sori. 
The question remains how this condition arose. Already, what has 
been seen in B. alpinum and in B. filiforme suggests very strongly the 
answer. The latter species, resembling Stenochlaena so closely as it does in 
habit and in leaf differentiation, provides the initial point of habit similarity. 
From this a general probability of similar characters of the fertile pinnae 
