Liverworts

Liverworts, or Hepatice, so-called from the form of the thalloid stems of some of the commoner genera (see Figs, on p. 151 in vol. ii.), form the lower class of the sub-kingdom Bryophyta (q.v.). Their vegetative structure is either frondose or thalloid (as in Marchantia), or foliose (as in Jungermannia). The thallus may be homogeneous, but is generally distinctly dorsiventral, the upper surface bearing curious stomata (q.v.), and the lower surface having root hairs and minute leaf-scales. The foliose forms are also dorsiventral, as though the stem is cylindric and ascending. It bears its leaves in two dorsiventral rows, sometimes with a third under row known as amphighastria, and it is the lower surface which roots. The leaves are but one cell thick, and have no veins. Most species can reproduce themselves by asexual gemmse, which are sometimes borne on the thallus in cup-like receptacles. Liverworts have also a sexual reproductive system. The antheridia are variously situated, but are always spheroidal, stalked, and enclosed by one layer of cells. They emit crowds of mother-cells of the antherozoids, and these last are clavate, spiral and bi-ciliate. The archegonia are surrounded by modified terminal leaves (the involucre) and by a tubular "perianth." They burst near their apex to form the calyptra, and the capsule (sporophore), which has originated from the fertilised germ-cell, generally divides into four valves. It bursts in many cases owing to the hygroscopic action of elongated cells with a double spiral filament in them which are known as elaters and are mixed with the spores. There is no character of universal application to separate them from mosses (q.v.).

Liverworts occur in moist situations all the world over, but have no economic applications.