124 HISTORY OF BRITISH FERNS. 



clestro3'ed by the autumn frosts. The form of the fronds 

 is lanceolate, more or less broad ; and they are supported 

 on stipites uliich are scaly at the base, and usually about 

 a third of the entire length of the fronds. The division 

 of the fronds is uhat is called bipinnate ; the pinnoe 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- 



