openings towards tho centre. Tho Banceinece have their sori connate
over tho whole under surface of the fertile fronds, which then
show long parallel lines of smaU round cavities, which are tho
openings of the concrete spore-cases.
The Polypodiacece offer so much variety of structure in their spore-
cascs that it becomes necessary to range the genera under eight
tribes or divisions, distinguished chiefly by peculiarities in tho form
of tho sporo-oases, in their number and position, or in tho structure
and development of tho annulus or ring, which latter presents some
curious differences. These tribes are as follows :—■
(1) Polypodinece, tho most extensive of all, in which tho spore-
oases arc almost equally gibbous or convex on both sides, with a
vertical and nearly complete ring, and bursting transversely at
a part on the anterior side, called the stoma, whore the stria; of tho
ring become dilated into elongate parallel cells.
(2) CyatheinecB, in which the spore-cases are sessile or nearly so,
and oblique-latcrally compressed, the nearly complete ring being, in
consequence, more or less obliquely vertical, that is, vertical below,
curving laterally towards the top, bursting transversely, and seated
on an elevated receptacle; they approach very near the Polypodinece
through some species of Ahophila, in which tho characteristic obliquity
of the ring is little apparent.
(3) Matoninece, consisting of a single species only, in which tho
ring is broad, suh-ohlique, and nearly complete, tho spore-oases
sessile, bursting horizontally, not vertically, tho sori dorsal and
oligooarpous, covered by umbonato-hemispherical indusia, which are
peltate, that is, affixed by a central sta lk ; they may be compared
to an inverted cup.
(4) Qleicheninece, in which the ring is complete and transverse,
either truly or obliquely horizontal, the spore-cases being globose-
pyriform, forming oligooarpous sori, i. e., sori consisting of but few
spore-cases (2-4 to 10-12), situated at tho back of the frond, sessile
or nearly so, and bursting vertically ; while tho fronds are rigid and
opaque, and are usually diohotomously-branchod.
(5) Trichomamnece, in which the ring rosomhlos that of tho
GleicheninecB, but tho sporc-casos aro lenticular, numerous, clustered
on an exserted receptacle, which is, in fact, a prolongation of the
vein boyond tho ordinary margin of the frond, so that the sori
become cxtrorso-marginal, or projected outwards as well as opening
outwardly; whlLo tho fronds arc poUuoid-membranaoeous.
(6) Schizceinecx!, in which tho ring is oithor horizontal or transverse,
hut situated quite at the apex of the oval spore-oase, which is, in
consequence, said to he radiate-striate at the apex; the spore-oase
is also sometimes resupinate, or turned upside down, so that tho
true apex is below.
(7) Ceratopteridinece, consisting of one or two, perhaps only a single
aquatic species, in which the spore-cascs aro sometimes furnished
with a very rudimentary ring, reduced, as in Osmundinece, to a few
parallel strise, sometimes furnished with a very broad and more
lengthened ring. In this little group, the spores themselves furnish
an exooUont supplementary oharaoteristio, being bluntly triangular,
marked with three series of conoentrio lines.
(8) Osmundinecs, which is distinguished from the rest hy having
its sporo-cases two-valved, bursting vertically at the apex; the ring,
moreover, is very rudimentary indeed, being reduced to a few
paraUol vertical strise (parallel elongated cells of the tissue) on one
side near the apex of the spore-oase. In aU the preceding tribes,
the spore-oases are not valvate, and consequently, when they open
for the liberation of the spores, they burst partially or irregularly,
and do not spht at tho top in two equal divisions, as occurs in the
OsmundinecB.