46 I. POLTPODIUM. 
fibrous roots. The fronds perish in winter when ex- 
posed to frost, and are renewed in May and June ; but 
nnder shelter become persistent: they generally ac- 
quire a drooping habit. The stipes is usually nearly 
equal in length to the leafy portion of the frond, and at 
the base is distinctly articulated with the caudex. The 
fronds are pinnatifid, with a more or less elongated ob- 
long outline, and vary from three to six, twelve, or even 
eighteen inches in length : the lobes are flat, linear- 
oblong, parallel, shorter towards the apex of the frond, 
obscurely serrated, and somewhat blunt- pointed, though 
occcasionally acute ; sometimes (var. bifidum) cleft at 
the end into diverging lobes; sometimes deeply and often 
bluntly serrated (var. serratuni). In the var. cambricum 
the frond is much broader, though not always ovate, as 
described, and the lobes themselves are irregularly jagged 
or slashed, so that it is twice pinnatind The venation of 
the common form is thus arranged : each lobe has a tor- 
tuous prominent mid- vein, from which alternately on 
either side the venules proceed ; these lateral veins are 
divided into four branches (veinlets) in vigorous fronds, 
or into three branches in smaller fronds, or in some of 
the very strongest fronds occasionally into five branches. 
The lowest venule, always on the anterior side, reaches 
about midway to the margin, and terminates when fenile 
in a sorus or cluster of spore-cases, or when barren in a 
club-like transparent head ; the other branches terminate 
in similar club-like heads, which form a line near the 
margin of the lobes. The sori are circular, entirely with- 
out an indusium, and at an advanced stage, often become 
crowded and confluent. The fronds are usually all fertile, 
the sori being produced on the upper part of each. 
This very common species is pretty generally distri- 
buted over the United Kingdom ; and is also met with 
in various other parts of Europe, in Asia, and in Africa. 
The decaying stumps and living trunks of trees, old 
thatched roofs, walls, moist rocks, and shady banks, are 
the positions which its creeping caudex prefers. 
