THE BRITTLE BLADDER FERN. 257 
occasionally sub-bipinnate, or rarely tripinnate. Pinne ovate-lanceo- 
late or oblong-lanceolate, with the pinnules usually distinet, but 
sometimes more or less decurrent or connected by the wing of the 
rachis. Pinnules, in the more typical forms, ovate at the base of 
the pinnz, oblong towards the apex, generally acute but sometimes 
bluntish; the larger ones deeply pinnatifid, with oblong toothed 
lobes, the smaller ones inciso-dentate or more shallowly toothed, the 
teeth generally acute. 
Venation of the larger pinnules consisting of a flexuous costa or 
midvein, from which a branch or vein proceeds along each lobe, 
giving off secondary branches or venules, mostly simple, one of 
which proceeds to the tip of each marginal tooth. The smaller 
pinnules more or less resemble the larger of these lobes, and are also 
similar as regards their venation. 
Fructification scattered over the whole back of the frond. Sori 
numerous, roundish, indusiate, medial on the veins and borne on 
nearly all their branches in fully fructified fronds, and hence in the 
more divided forms appearing to be scattered without order over the 
whole surface, but in the less divided forms, and often in the lobes of 
the larger ones, they are more evidently placed in a line towards the 
margin ; in the more typical forms they are situated nearer the midrib 
than the margin, and often in age become confluent. Indusium a 
smooth delicate hooded membrane, attached behind the sorus, either 
truncate and thus roundish, or prolonged at the point and thus 
acutely or acuminately ovate; at finst they are inflected forwards 
over the spore-cases, but they soon become reflexed and shrivelled ; 
the anterior margin is entire, or split into narrow segments. Spore- 
cases roundish obovate. Spores round or oblong, strongly echinate. 
Duration. The caudex is perennial. The fronds are annual, 
appearing in April or May, and quickly arriving at maturity ; these 
are followed by others in succession through the summer. The 
fronds are destroyed by the early frosts of autumn. 
When viewed as a collective species, and it cannot be satisfactorily 
viewed in any other light, this Fern is easily recognised by its small 
slender fragile bipinnate oblong-lanceolate fronds, and the peculiar 
hooded or semi-calyciform indusia, which in the early stages of 
VOL, II. s 

