













138 THE BRITISH FERNS. 
confined on this portion to the upper part of the pinne. Sori small, 
numerous, round, indusiate, seated at or near the apex of the venule, 
forming a line on each side of the midvein, and also of the vein of 
the auricle, often crowded, and sometimes becoming confluent; they 
are attached to the anterior venules of the fascicle whenever the 
veins are forked, but in the auricle several of the simple venules 
are fertile. Indusium firm, membranaceous, orbicular, peltate or um- 
bilicate. Spore-cases numerous, brown, roundish obovate. Spores 
roundish, ovate, muriculate. 
Duration. The caudex is perennial. The fronds, moreover, are 
persistent, and in mild seasons and sheltered situations, the plants 
retain their fronds in a tolerable fresh state far into or sometimes 
throughout the winter. Under shelter, the species is decidedly ever- 
green, the old fronds only gradually yielding, when the new ones 
become developed, which occurs about May. 
Although as regards P. angulare and P. aculeatum there is so 
close an affinity, that instances occur in which it is difficult to 
determine between them, yet, confining our view to the plants as 
found in Great Britain, such instances are rare, at least to those 
who have made themselves familiar with the aspect and charac- 
teristics of the plants. As to the application of the names, there is 
doubtless a certain amount of error and confusion, which it is hoped 
our autographic delineations may assist in correcting. When the 
inquiry is, however, extended, so as to include the closely allied exotic 
Ferns, the limits of the species become indistinct; and it is perhaps 
doubtful whether in this more comprehensive view,—at least by 
means of the mutilated examples alone available for examination in 
herbaria,—they can be defined with sufficient clearness to be kept 
permanently separate. The study of living plants may, indeed, afford 
_ other distinctive marks than those derived from form and texture, 
as in the case of Polypodium Dryopteris and. its ally, which have a 
different vernation, and in that of some forms of Lastrea Filiz-mas, 
among which differences both of vernation, and in the structure of 
the indusium occur. In reference to Polystichum angulare, there 
seems, with our present information, no mean between the two 
extremes of uniting the whole series from the simply pinnate P. 

