140 
THE GENERA AND SPECIES OF CULTIVATED FERNS. 
'ERTENSIA, Willdenow. —Name commemorative of F. C. Mertens, a Freneh botanist. 
Sori round or globose, naked or intermixed with hairs, medial, superficial, with three to eight, or some¬ 
times more, spore-cases in each sorus. Yeins simple or pinnatelv forked; venules 
direct, free, the exterior one fertile. Fronds rigid, from one to six feet high, 
many times dichotomously branched; pinnae pinnatifid, the segments linear, 
entire, uniform, smooth, glaucous, or villose, rarely dentate.—The species arranged 
under this genus are more readily recognized from the preceding by their habit 
than by any technical distinction; they have larger fronds, with plane segments, 
medial sori, and a more evident venation. Only a solitary species is at present 
in cultivation, JIT. fiabellata , of which Fig. 83 represents a small portion of a 
pinna (nat. size). 
1. JMJ. fiabellata , Desvaux, (Grleichenia, JR. Brown.) —An evergreen warm 
greenhouse Fern, a native of New Holland, Yan Diemen’s Land, and New Zea¬ 
land. Fronds rather erect, one and a half to two feet high, lightish green; stipes 
dichotomous ; primary pinnae opposite, flabelliform; ultimate pinnules lanceo¬ 
late, deeply pinnatifid, with linear segments slightly serrated on the margin. 
Spore-cases three to five inserted in each sorus. Fronds lateral, adherent to a 
creeping rhizome. This species has been in cultivation at Messrs. Loddiges for 
many years. 
Sub-order— 
-SCHIZjEACE-33. 
This group, consisting of a few genera widely differing in habit and general 
appearance from other Ferns, contains about forty species, technically character¬ 
ized by their spore-cases being oval or oblong, rarely globose, sessile ; open¬ 
ing vertically (lengthways) on their exterior side ; having a striated (rayed) 
apex, which is analogous to a transverse ring; and produced on contracted mar¬ 
ginal lobules, or special appendices, in the form of either simple, racemose, 
or paniculate contracted fronds or spikelets. Their nearest affinity is with 
Osmundaceae, with which they were formerly united; but Osmundaceae, as now 
restricted, differ essentially by having bivaived spore-cases, and materially in 
habit. 
L YGOD1TJM, Swartz. —Name derived from lygodes , flexible ; alluding to the 
twining habit of the plant. 
Sori on marginal appendices, forming numerous linear spikelets, which are 
composed of two series of indusiate imbri¬ 
cate cysts, each cyst or cell containing an 
oval sporangium, which is attached by its Fig. 83. 
interior side, and resupinate. Yeins (sterile) forked, free, or (fertile) pin¬ 
nate ; venules arcuate, bearing the spore-cases on their superior sides. Some¬ 
times the segments are contracted and form a dense sporangiferous rachis. 
Fronds twining, from two to twenty or forty feet high ; pinnae usually con¬ 
jugate, lobed, palmate, pinnatifid, pinnate or bipinnate. Rhizome decum¬ 
bent, casspitose, creeping.'—It very rarely occurs that habit stamps a genus 
with such a permanent feature as that by which the present is distinguished; 
the permanent twining habit is the natural character that distinguishes the 
genus. In this particular it is somewhat approached in Pteridae, by JPlaty- 
loma Jlexuosa , but that is easily known by being less scandent, and by the 
pinnae not being conjugate. There are many species belonging to the 
genus, chiefly found within or near the tropics, the same species being 
sometimes common to both hemispheres ; one species, L. palmatum, extend¬ 
ing to the parallel of 41° N. Lat., in the United States. Their twining 
habit renders the tropical ones well adapted for covering pillars, walls, 
trellis-work, or for training against the rafters in a moist stove, where 
they grow freely, and have a beautiful appearance, especially when loaded 
with fructification. Fig. 84 represents a pinnule of L. venustum (nat. 
size). 
1. L. palmatum , Swartz, (Hydroglossum, Willdenow). —A very elegant 
evergreen warm greenhouse Fern, from North America. Sterile frond gla- 
8 *. brous, very slender, about a foot long; pinnse conjugate, cordate, palmate^ 
membranous, five to seven-lobed, yellowish green above, rather glaucous beneath; lobes oblong, undulated, 
