POLYPODIUM. 
71 
fronds, and from its lower side chiefly the branching fibrous 
roots by which it clings to its support. The fronds, if 
exposed to frost, perish ; but if at all sheltered, they 
remain green during winter, and until after young ones 
have been produced, which happens generally towards the 
end of May. The stipes, or stalk, of the full-grown 
fronds is usually nearly equal in length to the leafy por- 
tion ; the entire frond measuring from six to eighteen 
inches in length. The leafy part of the frond is lance- 
shaped in outline, but cut in from the margin along both 
sides nearly as far as the midrib or rachis, and thus 
becomes what is called pinnatifid. The portions into 
which it is divided are called the lobes, or segments, or 
divisions of the frond ; and, in this case they are usually 
oblong in form, generally rounded at the end, but some- 
times tapering to a blunt point, and occasionally notched 
along the margin. Each lobe has a slightly wavy midvein, 
producing alternate lateral veins (venules), which generally 
have about four veinlets or little veins disposed alter- 
nately ; it is the lowest of these veinlets, on the side 
towards the point of the frond, which produces the sorus 
when it is present ; the rest, which are barren, terminate 
in club-shaped apices, which are very readily seen when a 
