BRITISH FERNS. 21 



The roots are brown, and often clothed with a thick pilosity. 

 The rhizoma is brown, and entirely covered with a densely 

 pilose cuticle^ which dries and peels off after one year's growth, 

 leaving the rhizoma smooth ; it is decidedly creeping, making 

 annual advances of great extent. The young fronds are thrown 

 out in May and June ; they arrive at maturity early in Sep- 

 tember, and retain their full vigour until the fronds of the 

 succeeding year make their appearance. The young fronds are 

 generally erect at first, but droop by degrees, and are always 

 pendent when mature : the rachis is green ; more than one-third 

 of its length is perfectly naked : the form of the frond is strap- 

 shaped and pinnatifid, and acute at the apex ; the pinnae are 

 nearly linear, and rounded at the apex ; their margins are more 

 or less serrated. The usual size is shewn in the detached 

 pinnulae, represented in the preceding page. The fronds are 

 fertile only, but the thecae are generally confined to its upper 

 part : when without fruit the imperfection arises from uncon- 

 genial situation, and the plant is not to be considered in a 

 perfectly natural and healthy state. 



The situation of the veins is shown in a detached pinnula 

 (see the preceding page) : the lateral veins are alternate, and 

 each is divided into four branches, three of which extend nearly 

 to the margin, and are incrassated at their termination; the 

 fourth is directed forwards, and its termination, which is nearly 

 equidistant from the midvein and margin, bears a circular 

 mass of thecae, which is entirely without indusium : a single 

 lateral vein, its four branches, the attachment of the thecae, 

 and the extent of the circular mass, indicated by a dotted 

 line, are shewn in the upper figure, to the right, of the 

 preceding page. 



In form of frond the Common Polypody is very uniform ; it 

 is however subject to a few variations, some of which are 

 remarkable; the detached pinnula* to the left, bearing the 

 masses of thecae, shows a strongly serrated variety, and the entire 

 frond to the right f has the termination of the pinnae bifid: 

 another variety, which is perfectly barren, is so strongly serrated, 

 that Linneus considered it a distinct species, and described it 

 under the name of Polypodium Cambricum : the identical frond, 

 named and described by that great naturalist, is now in the 



* See preceding page. t Ib. 



