124 HISTORY OF BRITISH FERNS. 
destroyed by the autumn frosts. The form of the fronds 
is lanceolate, more or less broad; and they are supported 
on stipites which are scaly at the base, and usually about 
a third of the entire length of the fronds. The division 
of the fronds is what is called bipinnate; the pinnae are 
always lanceolate, more or less drawn out at the point, and 
they are always again pinnate, though sometimes with the 
bases of the pinnules connected by a narrow leafy wing, 
but not so much so as to render them merely pinnatifid. 
The pinnules, however, are more or less lobed or pinnatifid, 
the lobes being sharply toothed in a varying manner. The 
delicate herbaceous texture of the frond renders the vena¬ 
tion very distinct; it consists, in each pinnule, of a wavy 
midvein, from which proceed alternate veins, which 
again produce alternate venules, and on the anterior side 
of this series of veins, at some distance from the margin, 
is borne an oblong sorus. In the larger and more divided 
pinnules the veining is more compound, and more than 
one sorus is produced from each primary vein, which 
thus becomes a midvein, with branches on a smaller scale. 
The sori are themselves oblong, a little curved, the basal 
ones usually hippocrepiform, or horseshoe-shaped, and 
they are covered by indusia of the same form as them- 
