Elementary Botany

by George Francis Atkinson

CLASS MUSCINEÆ (MUSCI).

524. Order Sphagnales.[30]—This order includes the peat mosses. There is but one family (Sphagnaceæ) and but a single genus (Sphagnum). The peat mosses are widely distributed over the globe, chiefly occurring in moors, or “bogs,” usually low ground around the shores of lakes, ponds, or along streams, but they often occur on wet dripping rocks in cool shady places. Small ponds are sometimes filled in by their growth. As the sphagnum growing in such an abundance of water only partially decays, “ground” is built up rather rapidly, and the sphagnum remains are known as “peat.” This “ground”-building peculiarity of sphagnum sometimes enables the plant (often in conjunction with others) to fill in ponds completely. (See Atoll Moor, Chapter LV.)

The gametophyte of sphagnum, like that of all the mosses, is dimorphic, but the first part (or protonema) which develops from the spores is thalloid, and therefore more like the thallose liverworts. The leafy axis (or gametophore) which develops from the thalloid form is very characteristic (see Chapter LV).

The archegonia are borne on the free end of the main axis, while the antheridia are borne on short branches which are brightly colored, red, yellow, etc. The sporophyte (sporogonium) is globose and possesses a broad foot anchored in the end of a naked prolongation of the end of the leafy gametophore. This naked prolongation of the gametophore looks like the stalk of the sporogonium, but a study of its connection with the sporogonium shows that it is part of the gametophyte, which is only developed after the fertilization of the egg in the archegonium. In the sporogonium there is a short columella, and the archesporium is in the form of an inverted cup.

525. Order Andreæales.[31]—This order includes the single genus Andreæa. The plants are small but form extensive mats, growing on rocks in arctic or alpine regions usually. They are sometimes found in great abundance on bare, rather dry rocks on mountains. The protonema is somewhat thalloid. The sporogonium opens by splitting longitudinally into four valves. An elongated columella is present so that the archesporium is shaped like an inverted test tube.

526. Order Archidiales.[32]—This order contains the single genus Archidium, and by some is placed as an aberrant genus in the Bryales. There is no columella in the simple sporogonium. The archesporium occupies all the internal part of the sporogonium, some cells being fertile and others sterile.

527. Order Bryales.[33]—These include the higher mosses, and a very large number of genera and species. The protonema is filamentous and branched except in a few forms where it is partly thalloid as in Tetraphis (= Georgia). (Tetraphis pellucida is a common moss on very rotten logs. The capsule has four prominent teeth.) In a few of the lower genera (Phascum, Pleuridium, etc.) the capsule opens irregularly, but in the larger number the capsule opens by a lid (operculum). A cylindrical columella is present, and the archesporium is in the form of a tube open at both ends. (Examples: Polytrichum, Bryum, Mnium, Hypnum, etc.)

528.

TABLE SHOWING RELATION OF GAMETOPHYTE AND
SPOROPHYTE IN THE LIVERWORTS AND MOSSES.

	GAMETOPHYTE. (Prominent part of the plant. Leads an independent existence.)				SPOROPHYTE (Attached to gametophyte and dependent on it for nourishment.)			Beginning of Gametophyte.
	Vegetative Phase	Vegetative Mulitipl- ication.	Sexual Organs.		Beginning of Sporophyte.	Sterile Part.	Fertile Part.
Riccia.	Thallus flattened, ribbon-like, forked, or nearly circular.	Sometimes by branching and dying away of older parts.	Immersed by surrounding, upward growth of thallus.		Fertilized egg. (Develops sporogonium.)	Wall of sporogonium, of one-layer cells.	Central mass (archesporium) develops .....	Spores.
			Antheridia, with spermatozoids.	Archegonia, with egg in each.
Marchantia.	Thallus flattened, ribbon-like, forked, male and female plants bear gametophores.	By dying away of older parts, and by gemmæ.	Borne on special receptacles on different plants.		Fertilized egg. (Develops sporogonium.)	Sterile part of stalked is stalk, wall of capsule of several layers, elaters.	Central part of capsule (archesporium) develops ..... and elaters.	Spores.
			Antheridia, with spermatozoids, borne on antheridiphores, or male gametophores.	Archegonia, borne on female gametophore (or archegoniophore), each with an egg.
Jungermannia (or Cephalozia, Porella, etc.)	A plant with apparent leaves and stem; margins of thallus have become cut into lobes. Male and female plants.	By dying away of older parts.	On different plants.		Fertilized egg. (Develops sporogonium.)	Sterile part of stalked capsule is stalk, wall of capsule of several layers, elaters.	Central part of capsule (archesporium) develops ..... and elaters.	Spores.
			Antheridia, with spermatozoids, in axils of leaves of male plant.	Archegonia, each with egg, on female plant.
Mosses. Mnium, Polytrichum etc.	Plant with apparent leafy axis, 3 rows of leaves (similar to jungermannia), borne on an earlier protonemal stage. Male and female plants.	By branching, by growth of protonema from axis, leaves, or even sporogonium. (In some genera by gemmæ.)	On different plants.		Fertilized egg. (Develops sporogonium.)	Sterile part of stalked capsule is stalk, wall of capsule of several layers, columella, lid, teeth etc., of the highly specialized capsule.	Cylindrical layer of cells around columella is the archesporium; it develops .....	Spores.
			Antheridia, with spermatozoids, at end of stem of male plant.	Archegonia each with egg, on female plant. (Calyptra found on sporogonium is remnant of archegonium.)