















78 THE BRITISH FERNS. 
and of the primary basal pinnules in the bipinnate fronds, consisting: 
of a flexuous costa or midvein, which, by a series of furcations, sends 
out a vein or venule towards each marginal tooth. If the pinnule is 
not deeply lobed, and the teeth are simple, the veins are also simple, 
and bear the sorus on their lower half, commencing iust above their 
base, and extending half-way to the margin ; but if the pinnule is 
lobed below, one vein passing off into each lobe divides into venules 
corresponding to the number of marginal teeth, and one or more of 
these venules in the larger lobes bears a sorus ; the smaller lobes are 
occupied by one fureation of the vein, which bears on its anterior 
side a long linear sorus, commencing near the midvein of the pinnule, 
and extending beyond the point of furcation. The venules reach 
up to the serratures, but not quite to their apex. 
Fructification throughout the back of the frond. Sori linear 
elongate, indusiate, on the anterior side of the veins near their 
base, and therefore central with respect to the pinnule; crowded, 
and soon becoming confluent. Indusium linear, entire, pallid, semi- 
transparent, and apparently grayish from the dark colour of the 
spore-cases showing through it. Spore-cases globose, shining brown. 
Spores ovate, angular, roughish. 
Duration. The caudex is perennial. The fronds are persistent 
through the winter, so that the plant is evergreen, and they are 
renewed annually. late in spring. 
The Black Maidenhair Spleenwort may be known from Asplenium 
danceolatum, which among British species it most resembles, by its 
long-stalked triangular fronds and elongated central sori. It may 
generally be known also by its conspicuously-stalked lower pinne, 
and by its surface being of a more glossy texture, and its substance 
more coriaceous. No other of the British species are so much 
divided, unless indeed acutum, which we place as a variety, is held 
to be distinct, and that may be separated by its caudate fronds 
and pinne, and its linear ultimate segments. 
The Black Maidenhair Spleenwort is a generally distributed plant, 
occurring on rocks, walls and sandy banks throughout England, 
Wales, and Scotland, extending to the Northern and Western Isles, 

