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HISTORY OF BRITISH FERNS. 
a broad-angled base, the lines of which usually exceed 
a right angle, and they are attached to the rachis of the 
pinnae by a short, distinct, slender stalk, which does not 
form a line with either margin. The pinnules have 
branched free veins ; and the sori are generally ranged 
in a row on each side the midrib, and are covered by a 
peltate scale or indusium. 
The highly-developed form of the species alluded to as 
having its basal pinnules deeply lobed, is the variety 
sub-tripinnatum. It is not uncommon, and does not 
differ materially in any other particular but that of the 
division of the pinnules ; being, however, rather more lax 
than the usual forms, it is one of the most elegant of them 
all. The variety decompositum is a form still more divided 
in the same way. 
The variety proliferum is another very elegant and 
highly-developed form. This has the pinnules narrowed 
and attenuated, more or less lobed ; and the stipes and 
rachis bear freely little buds or bulbils, which become 
young plants. It has been found in Devonshire. 
The variety imbricatum is a very remarkable form, 
differing from the type in the very narrow linear-lanceolate 
outline of the frond, as well as in having the pinnules, 
