


























228 THE BRITISH FERNS. 
under surface. Sori numerous, variable in size, distinct, round, 
indusiate ; medial sub-terminal or terminal, seated on the anterior 
basal venules in the less divided pinnules, and on the lowest anterior 
branch of the venules in the more compound pinnules; in the 
former consequently ranging in two lines, one on each side the mid- 
vein, and much nearer to it than the margin; in the latter forming 
two lines in a similar way along the lobes. Indusiwm reniform, rather 
large, convex, membranaceous, fringed around the margin with 
stalked glands; or sometimes smaller, flattish, and indistinctly glan- 
dular. Spore-cases numerous, brown, roundish-obovate. Spores 
roundish or oblong, muriculate. 
Duration. The caudex is perennial. The fronds are semi- 
persistent, and under shelter endure throughout the winter though 
decaying at the base of the stipes. The young fronds are produced 
in spring, and additional ones uncertainly during the summer. 
This is a most variable species, extremely difficult to understand, 
in consequence of its polymorphous character. It is more or less 
intimately united with two or three allied species, by means of 
transition forms, the kindred British plants being Lastrea emula, on 
the one hand, and that known as Lastrea spinulosa, on the other. 
The latter is distinguished readily enough by its creeping caudex, by 
the few broad pallid scales of its stipes, and by its entire indusium ; 
the former by its more strictly evergreen habit, by its lacerated 
scales, its anthoxanthoid fragrance, and by the absence of stalked 
glands from*the margin of its indusium. Lastrea emula may also 
be known by the concavity of its pinnee and pinnules; and even in 
the decay of its fronds it is peculiar, for whilst the forms of cristata 
and dilatata decay first near the base of the stipes, so that the 
fronds often fall while they yet appear green and fresh upwards, in 
emula the stipes continues firm, while the frond itself is undergoing 
decay, the disorganisation going on from above downwards, and not 
from below upwards. The distinguishing marks of Lastrea dilatata, 
in the group of which its variations form so large a proportion, are, 
its lanceolate dark-centred scales, and its gland-fringed indusia. 
The typical form of this protean species is generally distributed 

