Fig. 194.—Anthoceros lævis (nat. size): K-K capsules.
Fig. 195.—Plagiochila asplenioides: a unripe, and b an open capsule; p involucre. The ventral edge of each leaf is higher than its dorsal edge, and covered by the dorsal edge of the next one.
Fig. 196.—An elater with two spores.
Round the entire archegonium, (or group of archegonia, when several are developed on the same receptacle) a sheath—the involucre—is often formed, which persists, and encloses the base of the stalk of the sporangium, together with the sheath of the archegonium (Fig. [195] p). In the Marchantiaceæ each archegonium is enclosed in a loose investment, the perigynium, which is developed as an outgrowth from the cells of its stalk.
The majority of the Liverworts are found in damp and shady places, pressed to the substratum; a few are found floating in fresh water.
Family 1. Marchantieæ.
This embraces only forms with a thallus, which is more or less distinctly dichotomously branched, in some, one or two rows of thin leaves are situated on its under surface. On the upper surface of the thallus are found large air-chambers.
Order 1. Ricciaceæ. The sporogonia are, with the exception of a few genera, situated singly on the surface of the thallus, and consist only of a capsule without foot or stalk. They always remain enclosed by the wall of the archegonium (calyptra), and open only by its dissolution. Elaters are not developed. Some genera are found floating like Duckweed.—Riccia glauca grows on damp clay soil. R. fluitans and R. natans float in stagnant waters.