SCOLOPENDRIUM. 
157 
they are supported on shaggy stipes averaging about a third 
of their entire length. 
The fronds have a strong midrib or costa, extending 
throughout their whole length, from which are produced 
forked veins, the branches of which (venules) lie parallel, 
and proceed direct towards the margin, terminating just 
within the edge in a club-shaped apex. The veins are usually 
forked twice, but they are not constant to any exact num¬ 
ber of divisions. The sori, which are oblong patches of 
unequal length, lying in the direction of the veins at short 
intervals along the upper two-thirds of the length of the 
frond, are each composed of two proximate lines of fructi¬ 
fication laterally united; each of these lines, however, consists 
of a complete sorus, so that the two united are properly 
called a twin sorus. This is the mark of the genus Scolo- 
pendrium . This twin sorus is always produced between two 
fascicles of veins; that is, the lowermost venule produced by 
one vein, and the uppermost venule produced by the vein 
next below—these two venules lying, of course, contiguous, 
each become a receptacle upon which one of the two con¬ 
tiguous lines of spore-cases is produced. The indusia which 
cover these, have their attachment respectively on the upper 
and lower sides of their venules, the other edges overlapping 
