THE ALPINE SHIELD FERN. 



overlapping on flic upper part of the frond, though distinct ami sometimes distant below. They are 

 very rigid, and have scattered over their under surface numerous small hair-like scales. They are, 

 moreover, very shortly stalked or sessile, lanceolate-falcate, from three-quarters of an inch to an inch 

 and n quarter in length in the widest part, having an acute ]X>int, and an acute auricle at the base on 

 the anterior side, the base on Uie posterior side being obliquely slope*! or rounded off in all the upper 

 pinna*, but often produced into a posterior auricle in the lowest ones. The margin is serrated, the 

 serraturcs tipped by bristle-like processes, with minute intermediate teeth. 



Venation generally indistinct but often mora conspicuous in specimens from Wales, where the growth 

 seems more lax. There is a midvein extending to the n\>c\ of the pinna, and diverging from it, at the 

 very point where it enters the pinna, is a principal branch or win which extends to the apex of the 

 auricle ; this branch is phi natcly- forked on the same plan as the midvein, but on a smaller scale. The 

 rest of the reins on each side the midvein are pinnately forked, m,, they are branched, but the branches 

 are so placed that at each ramification the vein seems to have separate*! into two nearly equal and but 

 slightly diverging parts* In average specimens there are three or four of these ramifications to each 

 vein near the base of the pinna, then two, ami finally one in those near the apex. Tlio ivamAk* and 

 teinkts are lost in the substance of the frond just within the margin, one being directed iuto each 

 marginal tooth. In smaller specimens "the number of ramifications in the veins is fewer. 



Fructification on the back of the frond, and usually confined to the upper half, though sometimes 

 extending lower down, Sari round, iudusiate, forming a line on each side the midvein, halfway between 

 it and the margin, ami also in a similar way a line on each side the principal vein extending into the 

 auricle ; they are of variable size, but often large and crowded, and then generally become confluent in 

 age ; they are attached to the anterior branch of each fascicle of veins, ami are medial, seated nearer to 

 its base than its apex. tndtmum, or cover to the spore-cases, membranaceous, orbicular, umbilieate, 

 ami peltate, or attached to the receptacle by a short central stalk. Spww&m numerous, globose, 

 -stalked, deep brown. Spores small, round or oblong muriculate. 



Duration. The caudex is perennial, and the plant evergreen, the fronds, which appear, as is usual, 

 in spring, attaining their maturity by the autumn, and remaining in full vigour through the winter 

 onwards, 



This plant may be taken as the type of Polystichum, a genus established by Roth several years prior 

 to the publication of Aspidium, which has too long and too generally been allowed to supersede it It 

 is also the type of Potystichum in the restricted sense proposed by Schott, whose views we adopt. 



It is known from perfectly developed states of the cognate species by its being simply pinnate, but 

 imperfect and debilitated forms of them which sometimes occur are only pinnate, and from these it is 

 distinguishable with difficulty* The rigidity of texture, the strongly spinous margin, and the tendency to 

 imbrication in the pinme* offer the readiest marks of distinction from these anomalous congeners. 



Abnormal forms of this species are very rare. Sir. Wollaston has communicated notes of the two 

 following : — 



h mnllifidum : this has the fronds divided at the apex. It is probably rather to be considered as 

 an occasional and accidental variation, than as a true variety in the usual sense. 



2. proliferum: this form produces small bulbils in the axils of the lowermost pimne, and these 

 produce young plants when the fronds drop from decay. 



The cultivation of /\ Lonchilis will be noticed under that of the following species. 



