FILICINEIE. 
441 
ultimate branches of which the sporangia are developed as if they were metamorphosed 
laciniae. The ovoid or pear-shaped sporangia are sessile, the apex of each being occu- 
pied by a cap-like zone of peculiarly-formed cells. The dehiscence is longitudinal. The 
stem (also in Lygodium) does not branch much, and is but feebly developed. A single 
fibro-vascular bundle traverses the petiole. The leaves of Lygodium resemble twining 
stems. 
Family 3. Gleicheniaeese. The sessile sporangia are borne upon the dorsal surface 
of ordinary leaves. They form sori of usually three or four sporangia, and no indusium 
is developed. The sporangium has a complete transverse annulus, and longitudinal 
dehiscence. The stem is a thin, creeping rhizome. The lamina of the leaf is remark- 
able for its innovation. 
Family 4. Hymenophyllaceaa ^ The sporangia have an oblique or transverse 
complete annulus; and therefore burst with a longitudinal slit; they are formed on 
a prolongation of the fertile vein (the Columella)^ projecting beyond the margin of the 
leaf, which is surrounded by a cup-shaped indusium. The mesophyll of the leaves 
usually consists of a single layer of cells, -and is then necessarily destitute of stomata, 
which do however occur in Loxsoma on the leaf, which then consists of several layers. 
The stem is generally creeping and mostly very slender, and furnished with an axial 
fibro-vascular bundle. True roots are not present in all the species; where they 
are absent, the stem itself is clothed with root-hairs : a large number of species 
of Tr'ichomanes are described by Mettenius as rootless, and in these cases branches 
of the stem assume a deceptive root-like appearance. The development of the axes 
precedes by a long space that of the leaves ; several internodes have usually completely 
ended their growth while the leaves belonging to them are still very small ; and these 
apparently (or actually?) leafless shoots often branch further to a great extent. The 
formation of the tissue of these families shows also many peculiarities, concerning which 
reference must be made to Mettenius (Hymenophyllaceae, I.e.). The fertile end of the 
veins of the leaf projecting beyond its margin, the columella, elongates by intercalary 
growth, and the newly-formed sporangia are, in a corresponding manner, produced in 
basipetal succession. They are arranged in a spiral line on the columella. The almost 
sessile sporangia are biconvex, and are attached to the columella by one of their convex 
surfaces. The annulus projecting in the form of a cushion which separates the two 
convexities is usually oblique, and divides the circumference into two unequal portions. 
In Loxsoma the sporangia are pear-shaped and distinctly stalked. Paraphyses occur only 
in a few species of Hjmenophyllum. 
Family 5. Cyatheacese. The sporangia are shortly stalked and have a complete, 
oblique, eccentric annulus. They are borne upon a strongly-developed placenta 
forming a closely-packed sorus, which is either naked or invested by an indusium, which 
may be cup-shaped or completely encloses it. The genera Cibotium^ Balantium, Ahophila, 
Hemttelia, and Cyathea include the so-called Tree-ferns, Vv'ith a lofty, erect, unbranched 
stem, often thickly covered with roots, bearing at its apex a rosette of large usually 
compoundly pinnate leaves. 
Family 6. Polypodiaeese. The sporangia are borne in great numbers on the under 
surface of usually unmodified leaves, l^hey have a vertical incomplete ring, and they 
dehisce transversely. The following subdivisions of this family, which contains the largest 
number of species of any, may be distinguished : — 
(a) Acrostichex. The sori cover the surface and veins of the under side or of both 
sides, or are placed upon a thickened placenta which stands on the vein. There is 
no indusium. {Acrostichum, Polybotrya.) 
(b) Polypodies. The sori are rounded or linear, and terminal or lateral on the veins. 
They are naked. The leaf-stalk is either articulated to the stem {Polypodimn'), or is not 
{Pbegopteris.) 
^ [Prantl, Die Hymenophyllaccen, 1875.] 
