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HISTORY OF BRITISH FERNS. 
side, bluntish at the apex, and finely saw-edged along the 
margin. Some fronds are entirely barren, and these differ 
from the fertile ones only in having the leafy pinnules 
continued all the way to the apex, instead of having the 
apex contracted, and bearing the spore-cases. It is not 
always, however, that the spore-cases when present are 
produced at the apex of the frond ; abnormal developments 
are not uncommon, and in these cases any portion of the 
pinnules may be seen converted into spore-cases — some- 
times a few pinnae at the middle of the frond, while the 
apex is leafy ; sometimes the base of a pinna, while its 
apex retains the leafy form ; sometimes the base of a 
pinnule here and there, just its apex too, being broad and 
leafy; but the usual condition is to find a few of the 
shortened pinnae, which form the apex of the frond, con- 
tracted and soriferous throughout. 
The venation, as seen in the barren fronds, consists of 
a prominent midvein, bearing once- or twice-forked veins 
proceeding to the margin in direct lines. In the fertile 
parts of the frond, only the midrib of the pinnules is fully 
developed, and the spore-cases are attached to a small 
portion of the veins which becomes developed just tc 
serve as a receptacle. The spore-cases are subglobose, 
