BLACK SPLEENWORT. 
257 
a white, linear, narrow, scale-like involucre, also attached to the 
side of the veins : the clusters of capsules, together with their 
involucres, are situated rather nearer the midvein than the mar- 
gin, a character in which they differ from those of the species 
last described : the involucres open towards the midvein. As 
the capsules advance towards maturity, the involucre is lifted 
up and pushed away from its original situation, and finally it 
entirely disappears ; the form of the cluster of capsules is then 
lost, and, in very fruitful examples, the clusters become con- 
fluent, and nearly cover the underside of the frond. 
b 
Pinnae of Adiantam-nigrum^ (natural size). 
a, obtusum. h, oflScinarum. c, acutum. 
The superior length of the lower pinnae, — the oblique angle 
at which these, and indeed all the pinnae, are attached to the 
s 
