POLYPODIUM. 153 



roots by which it clings to its support. The fronds, if ex- 

 posed 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 portion; the entire frond 

 measuring from six to eighteen inches in length. The 

 frond itself, that is, the leafy part, 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 sometimes tapering to a blunt 

 point, and occasionally notched along the margin. 



Each lobe has a slightly tortuous midvein, producing al- 

 ternate lateral veins (venules), which generally have about 

 four veinlets or little veins disposed alternately ; it is the 

 lowest of these veinlets, on the sides towards the apex of 

 the frond, which produces the sorus when it is present ; the 

 rest, which are barren, terminate in club-shaped apices, 

 which are very conspicuously seen when a fresh frond is 

 held up between the eye and a strong light. Most of the 



