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Ribbon-like or Thalloid Hepatics

Genus MARCHANTIA, (L.)

Marchantia polymorpha (See Colour Plate XIII) is a good example of a thalloid form, and from it one may learn, without a microscope, the principal parts.

The plant itself lies flat upon the earth and has a distinct upper and lower tissue.

The lower tissue develops short root-like hairs which serve to anchor the plant.

The upper tissue appears as if marked off into small rhomboidal spaces in the centre of each of which a pore may be seen.

Little cups are often present on the upper surface, with green disks (gemmae) in them.

Upright umbrella-like growths on which are borne the male and female organs are found also on the upper surface.

The male peduncle is capped with a flat, slightly lobed receptacle. The female peduncle is capped with a receptacle bordered with deep finger-like lobes.

The male organs (antheridia) are developed in the upper surface of the scalloped receptacle.

The female organs (archegonia) are developed on the under surface of the receptacle bearing the finger-like lobes.

Spore-cases filled with spores and spirally twisted threads (elaters) later occupy the place of the archegonia between the long lobes.

A veil (calyptra) surrounds the spore-case.

A false perianth surrounds the veil.

A fringed covering (involucre) encloses all the spore-cases between two lobes. When the spore-case is mature, it bursts irregularly for the scattering of the spores.

The spore germinates to form one cell or a small group of cells (protonema) from which later will be developed the plant already described.

Marchantia polymorpha, (L.)

Habit and habitat.--Along wet banks, in bogs, beside streams, about green-houses, and on damp ashes on the shady side of houses.

Name.--The generic name Marchantia was given by the son in honour of his father, Nicholas Marchant, a French botanist who died in 1678. The specific name polymorpha is compounded of the Greek, many, and, form.

Plant (gametophyte).--Peculiar dull-green, with broad ribbon-shaped thallus generally once or twice forked. Costa or mid-vein broad. Upper surface divided off into rhomboidal spaces (areolae). One stoma or pore in the centre of each rhomboidal space. Gemmae cups, saucer-shaped with toothed margins, are often present.

Section of plant.-

(1) Shows well-marked epidermis.

(2) Shows that each pore leads into an air-chamber.

(3) That the side walls of each air-chamber support the epidermis as a roof.

(4) That cells containing chlorophyll spring up from the floor of each chamber. These cells assimilate gases which enter the air-chamber through the pores, they also take in oxygen gas and give out carbon-dioxide gas. The floor-cells transmit or store up food.

Habit of flowering.--Antheridia or male organs are imbedded in the upper surface of a shield-shaped, radially lobed disk supported by a peduncle and bearing scales on the under surface. This male receptacle (androecium) grows from the upper surface of the thallus. Archegonia or female organs are borne on the under side of a radially lobed disk supported upon a peduncle on the upper surface of the thallus. The lobes are finger-like, 8 to 11, usually curved downward.

Section of male disk.--Shows antheridia concealed in depressions in the surface of the disk.

Male flowers (antheridia).--Oval upon a pedicel (seta). Section shows a wall and numerous cells containing spermatozoids, each with two fine cilia.

Section of female disk.--Shows archegonia on the under side of the disk.

Female flowers (archegonia).--Flask-shaped. Cuts 1, 2, 3, 4, 5, 6, 7, 8, show stages in development. Section in early stage, 3, shows a wall of cells; an egg-cell and canal-cell in the enlarged base of the flask; a canal in the neck of the flask and the summit of the neck closed. Section in a later stage, 6, shows a wall of cells: the egg-cell rounded up; the canal-cell shrivelled; the canal open at the summit of the neck.

Development of sporophyte.--A section, 7, of the archegonium after the spermatozoids have entered and fertilised the egg-cell shows the wall of the enlarged portion of the flask surrounded by an involucre, made up of segments, awl-pointed and finely cut, into an irregular fringe often reddish in colour; the egg-cell is divided into eight cells; the summit of the neck is shrivelled. Section later, 8, shows the eight cells multiplied to form an upper portion, the future spore-case and a lower portion, the future foot and pedicel.

Spore-case.--At maturity is exserted, when it bursts some-what irregularly to discharge its spores.

Spores.--Yellow, nearly smooth, mingled with twice-spiral elaters.

Gemmae.--Receptacles bowl-shaped, on the upper-surface of the thallus, and open at the top. Gemmae flat, upright cellular bodies with two indentations at the sides, the growing points. When gemmae germinate, the side toward the light develops pores (stomata) for the admission of gases and for the egress of gases and water vapour. If germination takes place on land, the stomata are on the upper surface, but if in water lighted from below, then they are on the under surface. Gemmae are a means of reproducing plants.