72 
HISTORY OF BRITISH FERNS. 
fresh frond is held between the eye and a strong light. 
Most of the fronds of this kind of Fern produce fructifica- 
tion, which, however, is usually confined to the upper half 
of the fronds, and has generally become mature by the end 
of September. 
The most remarkable variety is cambricum, the Poly- 
podium cambricum of Linnmus, commonly called the 
Welsh Polypody. The lobes of the frond in this variety 
are broader, and, instead of being simple, are deeply and 
irregularly lobed a second time, the segments being rather 
sharply toothed. This form, which is certainly only a 
variety of the common Polypody, is always found without 
fructification. Under slight shelter, where its fronds are 
persistent, it is one of the most beautiful of what are called 
hardy Ferns. The Irish Polypody, an equally elegant 
form, called semilacerum, is found in Ireland and else- 
where ; the lower half of its fronds are a second time 
lobed, and the upper half usually fertile, and not twico- 
lobed. The variety omnilacerum is a fertile form re- 
sembling cambricum^ found in Herefordshire. These 
three have a certain general resemblance. 
There are many other varieties which have been pro- 
posed ; of which we may mention — bifidum, in which the 
