164 
HISTORY OP BRITISH PERNS. 
thirds the height of the fertile ones, assume a spreading or 
horizontal position, and are attached to the caudex by a 
very short scaly stipes. The fertile ones, which are situated 
in the centre of the tufts, are erect, from one to two feet 
high, the stipes, which is sparingly furnished with long 
pointed scales, being nearly half the length, and of a dark- 
brown colour. 
The veins are not very evident in the fertile fronds, on 
account of the contraction of the parts, but they resemble 
those of the barren ones, except in having a longitudinal 
venule on each side the midvein, forming the receptacle 
to which the spore-cases are attached. The midvein is 
prominent, and produces a series of veins on each side, 
these becoming forked, and extending almost to the margin, 
terminating in a club-shaped head. In the fertile fronds 
the veinlets are necessarily shorter, and connected, as 
already mentioned, by the longitudinal venules which 
bear the fructification. The spore-cases are thus arranged 
in two linear sori, one on each side the midvein; 
these are distinct while young, but often become con¬ 
fluent, covering the whole under-surface of the pinnas. 
The indusia, by which they are first covered, when 
mature, burst along that side towards the midrib, and 
