Order 1. =Ophioglossaceæ.= The prothallium differs from that of all
other Ferns in being _subterranean_, _free from chlorophyll_, _pale_
and _tuberous_. The stem is extremely short, with short internodes,
most frequently unbranched, vertical, and entirely buried in the ground
(Fig. 208 _st_). In several species (among which are the native ones)
one leaf is produced every year, which has taken three to four years
for its development. In _Botrychium_ a closed, sheath-like basal part
of each leaf covers the subsequent leaves during their development. In
_Ophioglossum_ and others each leaf has at its base an intrapetiolar,
cap-like sheath, which protects the succeeding leaf. The leaves are
of two kinds: (_a_) foliage, which in _Ophioglossum vulgatum_ are
lanceolate and entire, but in _Botrychium_ however, are pinnate (_b_
in Fig. 208 _A_, _B_); and (_b_) fertile, which are found facing the
upper side of the foliage-leaves. These latter in _Ophioglossum_ are
undivided and spike-like (Fig. 209 _A_), but pinnate in _Botrychium_
(Fig. 208 _B_). Each foliage and fertile leaf are branches from the
same petiole. The large sporangia are placed laterally, and open by
two valves. No annulus is formed (Fig. 209).--_Ophioglossum_ reproduces
vegetatively by adventitious buds on the roots.
[Illustration: FIG. 208.--_A Ophioglossum vulgatum_
(Adder’s-tongue); _B Botrychium lunaria_ (Moonwort), both
natural size; _r-r_ roots; _bs_ leaf-stalk; _st_ stem; _b_
foliage-leaf; _f_ fertile leaf.]
[Illustration: FIG. 209.--Fertile leaf of _Ophioglossum_.]
Three genera with about twelve species.
Order 2. =Marattiaceæ= are tropical Ferns, whose gigantic leaves
resemble those of the Polypodiaceæ, but have stipules in addition.
The sporangia are grouped in sori, situated on the lower side of the
leaves, the sporangia in each sorus being arranged either in two rows
or in a ring. In _Angiopteris_ they are isolated (Fig. 210 _A_),
but in the other species (_Kaulfussia_, _Danæa_, _Marattia_), they
are united, and form “synangia” divided into a number of chambers
corresponding to the sporangia. These open by clefts or pores.
_Marattia_ presents the highest development, as its sporangia are
completely united in a capsule-like synangium, which is closed until
maturity, and then opens by two valves. In each valve there is a row
of three to eleven sporangia, each opening by a slit towards the
inside (Fig. 210 _B_, _C_). An indusium encloses the sorus, except in
_Kaulfussia_; it is formed of flat and lobed hairs, which resemble
the hairs of the other portions of the leaves. In _Angiopteris_ and
_Marattia_ the indusium is very rudimentary; in _Danæa_ it forms a kind
of cupule.
The numerous fossil Marattiaceæ (15 genera, with 98 species)
present similar differences to those now living, but more
various forms are found, for example, with solitary free
sporangia. Those now living are the last small remnant (4 genera
with only 23 species) of a once dominant family, which existed
from very early times, and whose culminating point was reached
in the Kulm and Coal periods.
The Ophioglossaceæ appear also in the Kulm and Coal periods,
and were about as numerous as at the present time (presumably 2
genera, with 19 species). Leptosporangiate Ferns appear however
to have occurred first of all in the Trias-formation.
[Illustration: FIG. 210.--Sporangia of the Marattiaceæ: _A_
_Angiopteris_; _B_ and _C Marattia_; _C_ is a half sorus with
nine sporangia, each of which has opened by a longitudinal cleft.]