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The spores of Ceratopteris thalictroides are large (104 × 128 μ), trilete, with a costate exine and devoid of perine. At germination a rhizoid is produced at the proximal pole, followed by a short uniseriate germ filament lateral to it. Formation of a prothallial plate is initiated by longitudinal divisions in the intercalary cells of the germ filament, and soon a strap-like plate is developed. The thallus broadens and becomes spatulate, but is devoid of any meristem. A pluricellular meristem is later differentiated from lateral marginal cells on one side of the thallus away from the anterior region. The meristematic region becomes notched and later cordate. The anterior half of the thallus expands and develops into a broad flat wing while a smaller, often uplifted wing is developed posterior to the meristem. A midrib is formed behind the meristem when the prothalli are ca. 5 weeks old. The mature prothallus is devoid of trichomes, asymmetrically cordate, with a large, spreading wing and a smaller, often curled and cornucopia-shaped wing lifted up from the substratum. The midrib is thin and bears rhizoids and archegonia on the lower surface. Antheridia are restricted to the wings and are common marginally; they are embedded in the prothallial tissue, and consist of a central mass of spermatozoids surrounded by a basket-shaped, thin, basal cell, a narrow ring cell, and a solitary disk-shaped cap cell. The latter opens like a lid at antheridial dehiscence. The first wall formed in the antheridial initial is basket-shaped and the second wall is nearly flat. Development of the embryo is of the common type in leptosporangiate ferns. The first juvenile leaf is naked, with a spatulate lamina supplied by a solitary vein, and associated with the first root. One or two thick multicellular hairs are produced at the base of the second leaf and, in the succeeding leaves, these appendages are palea-like. A stem apex becomes evident usually only after the fourth leaf is developed. All early juvenile leaves are subsessile with entire lamina. The venation becomes reticulate in the second or third juvenile leaf. It is concluded that Ceratopteris is more closely allied to Anemia and Mohria than to other genera of ferns.

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SUMMARY The rhizome of 12 species of Bolbitis and 7 species of Egenolfia studied is creeping, more or less flattened dorsiventrally, often tenaciously attached to the substratum by wiry roots, and brittle. Basally attached, auricled paleae, bearing terminal and marginal glandular hairs clothe the rhizome. The ground tissue of the rhizome is parenchymatous: slender sclerenchyma strands are scattered in the ground tissue (except in B. presliana and E. helferiana). The vascular cylinder is solenostelic with a broad, intact, often gutter‐shaped, root‐bearing, ventral region, and the dorsal region highly dissected by 2 (3 or 4 in some spp.) longitudinal rows of large leaf gaps. The leaf traces are multiple strands: associated with each leaf trace is a solitary branch trace, generally bearing one root trace and originating either independently from the abaxial end of the leaf gap or along with the abaxial bundle of the leaf trace. In some species, either the branch‐ or the root‐trace, or both, is vestigial. Leaves are restricted to the dorsal surface of the rhizome and are usually in 2 but may be in as many as 4 rows. They are once‐pinnate, and dimorphic. The stipe and rachis possess a pair of longitudinal grooves on the adaxial surface. Many vascular bundles ascend the rachis: the 2 adaxial bundles are larger than the others. In the rachis the adaxial ones fuse together to form a median dorsal bundle and the others fuse together to form a median ventral bundle: toward the apex of the leaf both merge together. The pinna traces are paired strands originating from the adaxial bundle and the bundle next to it. Venation is free in Egenolfia (except the tendency for areole formation in E. bipinnatifida), and goniopteroid with variation according to species in Bolbitis. The terminal pinna is prolonged in many species. A sub‐apieal vegetative bud is found laterally on the dorsal surface of the midrib on the terminal pinna; in some species similar buds are borne also on the lateral pinnae. The fertile leaves are seasonal and lamina of the fertile pinnae is highly reduced. Sporangia are acrostichoid in distribution, and uniseriate hairs occur, mixed with them. The sporangial stalk is 3 cells thick near the capsule, the 3rd row being short and formed secondarily as a protrusion from the proximal end of the capsule wall, below the stomium.

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