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78 THE BRITISH FERNS. 
plaeed near the margin of the segments. In the subtripinnate 
fronds, which have the segments more or less doubly toothed, the 
venules are occasionally forked, the anterior veinlet, or sometimes 
both, bearing a sorus; in these examples the sori, three or four on 
each side the segment, form tolerably distinct submarginal lines. 
The sori are in all cases attached near to, but below, the apex of the 
vein, which reaches to the margin. 
Fructification on the back of the frond, occupying the upper two- 
thirds of its length. Sori small, circular, usually distinct, but 
sometimes crowded, and becoming confluent; usually naked, but 
sometimes (though rarely and only in abnormal-looking sori) the 
spore-cases are somewhat lateral, and a membrane, which appears to 
be an abnormal development of the dilated portion of the vein 
which forms the receptacle, is produced, simulating an abortive or 
spurious indusium. Spore-cases roundish-obovate, brown, numerous. 
Spores roundish or oblong, somewhat muriculate. 
Duration. The caudex is perennial. The fronds are annual, 
growing up in April or May, and perishing early in autumn. 
The Fern is at once distinguished among the British Polypodies 
by its short thick erect tufted caudex, and by the lanceolate form, 
and bipinnate or tripinnate mode of division of its fronds. It has 
certainly a general resemblance to Athyrium Filix-femina, with 
which it appears to have been very generally confounded, but the 
fructification, as usually borne, is very different, and even the resem- 
blance of the frond to that species is not found on comparison to be 
so close as a first glance suggests. 
The short massive caudex with terminal adherent fronds, would 
lead those botanists who derive generic distinctions from the mode 
in which the plant is developed, to separate the present species 
from Polypodium. Of those who do so, some refer it to the genus 
Phegopteris, in company with the other British species we retain in 
the Phegopteris section of Polypodium. Mr. Newman, however, 
creates for it a new genus, which he calls Pseudathyrium. We 
think it may be safely retained in Polypodium, as here understood. ` 
The supposed ‘indusia,’ ascribed to this plant, which may be 
noticed both in the species itself, and in the variety flexile, are only 

