THE ALPINE SHIELD FERN. 119 
fascicle of veins, and are medial, seated nearer to its base than its 
apex. Indusium, or cover to the spore-cases, membranaceous, 
orbicular, umbilicate or peltate, i. e. attached to the receptacle by a 
short central stalk. Spore-cases numerous, globose, stalked, deep 
brown. Spores small, round or oblong, granulate. 
Duration. The caudex is perennial, and the plant evergreen ; the 
fronds, which appear, as is usual, in the spring months, attain their 
maturity by the autumn, and remain in full vigour through the 
winter onwards. 
This plant may be taken as the type of Polystichum, a genus 
established by Roth almost contemporaneously with the publication 
of Aspidium, with which in its original form it is synonymous, and 
which has generally been allowed to supersede it where the genus 
has been preserved in its entirety. The present species is also the 
type of Polystichum in the restricted sense proposed by Schott, whose 
views we adopt. 
Polystichum Lonchitis is known from perfectly developed states of 
the cognate species by its being simply pinnate, but from young and 
imperfect or debilitated forms of the latter, which sometimes occur, 
and are only pinnate, it is not so readily distinguishable. The 
rigidity of texture, the strongly spinous margin, and the tendency 
to imbrication in the pinnae, offer the readiest marks of dis- 
tinction from these anomalous congeners which are imperfect forms 
of P. aculeatum. 
This species seems less liable to sport into abnormal forms than 
the others of the genus. It does occur sometimes with the fronds 
divided at the apex, but this is merely an occasional and accidental 
variation. The plants, moreover, sometimes produce small bulbils 
in the axils of the lowermost pinne, from which young plants spring 
up. This quality of producing bulbils seems to be the result in great 
measure of certain little understood peculiarities of cultivation or 
situation ; for while with some cultivators many of the British species 
prove bulb-bearing, the peculiarity seldom occurs with others. 
This Fern may be considered as an alpine rock-plant. It is 
plentiful on the mountains of the Scottish Highlands, where it has 

