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.
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.
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.
