IX 
DEFINITIONS. 
Febks are flowerless plants, consisting of leafy fronds, spirally 
nnfolding, and traversed by veins, which, from definite parts on 
the under surface of the frond (rarely on both), produce unilo- 
cular or rarely multilocular cases (sporangia), containing repro- 
ductive spores. 
The fronds vary in form, size, and texture, and are produced 
either from the sides of a special rhizome , and articulated with it 
(. Eremobrya ), or from the apex of a sarmentose or cormiform, 
often arboreous caudex, with which their bases are adherent 
(Desmobry a). They are furnished with a footstalk (stipes), or 
are leafy to the base (sessile) . They vary from less than an 
inch to fifteen or twenty feet in length, and from linear-filiform 
to broad-elliptical or deltoid ; they are simple entire, or once or 
more times pinnate, or decompound branched (pinnate, bi-tri - 
pinnate, etc.) 5 the ultimate pinnae or segments are analogous in 
structure to a simple frond, being entire, sinuose, lobed, equally 
or unequally pinnatifid, or variously laciniated, sessile or petio- 
lated, and either articulated or adherent with the rachis. In tex- 
ture they vary from thin, membranaceous, and pellucid, to thick, 
coriaceous, opaque, and rigid, and are either smooth or furnished 
with different kinds of glands, hairs, or deciduous membranous 
scales. In some the stipes and primary branches (rachis) are 
