University
of Winnipeg
Kent Simmons
Algae,
Fungi and Mosses Lab Manual Table of Contents
Order Marchantiales
Marchantia sp.
One of the most familiar thalloid liverworts is Marchantia
sp. This is a fairly widespread, terrestrial genus that grows moist soil and
rocks. Internally the gametophytes may be stratified into several tissues. The
uppermost layers of cells are photosynthetic, and are contained in distinct air
chambers which are open to the air through small pores in the upper surface.
Ventral layers of cells in the thallus are used for storage, and usually don't
contain chloroplasts. On the under surface they have rhizoids and multicellular
scales.
Marchantia sp. has its gametangia restricted to
specialized erect structures called "gametophores". The male
and female gametophytes can readily be identified by their gametophores, which
are structurally quite distinct from one another. The antheridia are borne on
disk-headed stalks called "antheridiophores", and the
archegonia are borne on umbrella-headed stalks called "archegoniophores".
The sporophytes of Marchantia sp. consisting of a
foot, a short stalk or seta, and a capsule or sporangium. In addition to spores,
the mature sporangium contains elongate cells, celled "elaters",
which have spirally arranged hygroscopic (moisture-absorbing) wall thickenings.
These elaters aid in spore dispersal after the capsule bursts open (dehisces)
into a number of petal-like segments.
Fragmentation constitutes the principal means of asexual
reproduction in the liverworts. Another fairly widespread means of asexual
reproduction in the liverworts and mosses is the production of "gemmae".
These are minute, multicellular, undifferentiated bodies that can give rise to
new plants. In Marchantia sp. the gemmae are produced in special cup-like
structures called gemmae cups located on the dorsal surface of the gametophyte.
Transverse section of Marchantia sp. gametophyte.
Male and Female gametophytes of Marchantia sp.
showing antheridiophore and archegoniophore.
Long section of Marchantia sp. sporophyte.
Cross section of Marchantia sp. Gemmae Cup with gemmae.
Marchantia sp. Gemmae Cup with gemmae.
Life cycle of Marchantia sp.
Marchantia sp. Antheridiophores.
Cross section of Marchantia sp.
Antheridiophore.
Marchantia sp.
Archegoniophore
Cross section of
Marchantia sp.
Archegoniophore
- Examine the preserved material of the Marchantia sp.
life history. Note the vegetative thallus with dichotomous branching, costa,
pores, rhizoids, scales, gemmae cups, and gemmae. Also note the antheridiophore,
antheridial discs, and spots were antheridia are submerged in chambers. Note the
archegoniophores, archegonial discs, with attached sporophytes.
- Examine the prepared slide of the cross section of the
thallus of Marchantia sp. and note the vegetative differentiation into
epidermis, scales, rhizoids, air chambers, chlorophyllous filaments,
parenchymatous tissue, pores, gemmae cups with gemmae. Examine the slide of a
developing archegoniophore and note the archegonia with venter, egg, and neck
canal cells. Examine the slide of the antheridiophore and note the antheridia,
antherzooid (sperm) mother cells, and jacket cells. Finally, examine the slide
of the archegoniophore with a long section of a sporophyte, and note the foot,
seta, capsule, spores, elaters and calyptra.
Conocephalum sp.
This is the largest thalloid liverwort in North America.
Examine the preserved material and compare this genus with Marchantia.
Note that the antheridiophore is lacking and the antheridia are borne on a
sessile pad. Also examine the prepared slide of the same stage.
Riccia sp.
This genus contains a number of morphologically dissimilar
species. On the basis of the sporophyte structure, Riccia and Ricciocarpus
are among the simplest of liverworts. Some species of Riccia are aquatic,
although most are terrestrial. Riccia sp. gametophytes may be either
unisexual or bisexual. The sporophytes are deeply embedded within the
dichotomously branched gametophytes, and consists of little more than a
sporangium. No special mechanism for spore dispersal occurs in these sporophytes.
When the portion of the gametophyte containing the mature sporophytes dies and
decays, the spores are released.
- Examine the live or preserved material of Riccia
fluitans a free floating aquatic liverwort. Also examine the slides of
another species of Riccia and note that neither the antheridia nor the
archegonia are produced on stalked structures but are embedded in groves on the
thallus.
antheridia
archegonia
- Examine the slide of the sporophyte and compare this
structure with that of Marchantia.
Ricciocarpus sp.
- Examine the preserved material and note the grooves on the
thallus where the reproductive gametangia are embedded. Also note the ventral
scales.
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University
of Winnipeg
Kent Simmons
Algae,
Fungi and Mosses Lab Manual Table of Contents