3. Vegetative Structure: External Features
▪ It occurs in moist, shaded habitats in sub-
tropical and warm temperate regions.
▪ The gametophyte are dorsiventral and are often
rosette-like.
▪ On the ventral surface, many smooth walled
rhizoids are present which help in fixation.
4. ▪ Scales and tuberculate rhizoids are absent.
▪ Some species of Anthoceros are unisexual and
others are bisexual.
▪ The antheridia and archegonia are sunken on
the dorsal surface of the gametophyte.
▪ Numerous sporophytes may develop on the
same gametophyte.
6. ▪ Thallus is not differentiated into photosynthetic
zone and storage zone.
▪ All cells are green and contain chloroplasts.
▪ Chloroplasts are associated with pyrenoids which
is a unique feature of Anthocerotales.
▪ There are no air chambers or pores.
▪ Schizogenous cavities filled with mucilage are
present. These are often inhabited by Nostoc
(cyanobacteria), which supply nitrogen through
nitrogen fixation to their host plants.
8. ▪ Fragmentation: occurs through progressive death
and decay of posterior portion of thallus.
▪ Tubers: develop at the end of growing seasons.
Under unfavorable conditions, they perennate and
grow in the next growing season.
▪ Gemmae: borne on short stalks on dorsal surface
and along margins of thalli. They detach and
germinate to produce new plants.
▪ Persistent growing apices
Vegetative Reproduction
9. ▪ It is oogamous type.
▪ Male sex organs are antheridia and female are
archegonia.
▪ Many species are monoecious while some are
dioecious.
▪ Formation of sex organs are dependent on specific
photoperiods.
▪ Anthoceros being a short day plant, sex organs
develop in winters.
▪ Antheridia develop much earlier to archegonia.
Sexual Reproduction
10. ▪ Occurs on dorsal surface of thallus in an acropetal
succession inside closed cavities called antheridial
chambers.
▪ It is differentiated into a long stalk and clubshaped
body.
▪ The stalk is multicellular, slender and consisted of 4
vertical rows of elongated cells.
▪ The club shaped body of antheridium has single
layered sterile jacket enclosing a mass of androcytes
which metamorphose into biflagellated curved
anthrozoids.
Sexual Reproduction - Antheridia
13. ▪ These are embedded on dorsal surface of thallus
in an acropetal succession near growing point.
▪ The archegonial chambers are absent.
▪ It is flask shaped consisted of neck and venter.
▪ It contains 4-6 neck canal cells, a venter cell and an
egg.
▪ At maturity, the neck canal cells disinitegrate and
become mucilagenous.
▪ There are no jacket cells covering the Archegonia.
▪ Cover cells or Lid cells are found at the tip of
Archegonium.
Sexual Reproduction - Archegonia
15. ▪ The anthrozoids swim in water film.
▪ Some of these reach mature archegonium.
▪ The mature archegonium is characterized by
mucilaginous mound at its apex.
▪ The antherozoids pass through mucilage and enter
its wide open canal.
▪ Single antherozoid fuses with egg to form a diploid
zygote.
Fertilization
17. The sporophyte is differentiated into 3 distinct regions:
▪ Foot: It is basal, bulbous parenchymatous structure
found deeply embedded in the gametophyte. It helps
in attaching the sporophyte to gametophyte and in
absorption of water and nutrients from it.
▪ Intermediate or intercalary zone: A narrow zone of
meristematic cells located between the basal foot and
the upper capsule. These cells help in the continuous
growth of the sporophyte.
▪ Capsule: It is the fertile, major and conspicuous part of
the sporophyte which is long and cylindrical. It is green
when young, but turns grey or brown on maturity.
Sporophyte/Sporogonium
18. The capsule is composed of the following structures:
a) Columella: It is central solid core of sterile cells, consisting of 16
vertical rows of cells. It extends from the base to almost to the
tip of the capsule.
b) Sporogenous tissue: It is the mass of fertile spore-forming cells
surrounding the columella, like a dome. At the base of the
capsule, it is single layered and called archesporium. It becomes
2-4 layered and develops into diploid spore mother cells
upwards. Towards the tip of the capsule, the spore mother cells
divide by meiosis and produce haploid spores.
Sporophyte/Sporogonium
19. • Capsule wall: It is the outer wall of the
capsule which is 4-6 layers in thickness. The
outermost layer is called epidermis which is
interrupted by stomata. The inner layers
consist of chlorenchymatous cells and are
photosynthetic.
20.
21.
22. Structure of Spore:
• The spores are haploid, uninucleate,
semicircular with a conspicuous triradiate
mark. Each spore remains surrounded by
two wall layers.
• The outermost layer is thick ornamented
and is known as exospore. It varies in colour
from dark brown to black.
• The inner layer is thin and is known as
endospore. Wall layers enclose colourless
plastids, oil globules and food material.
23. Germination of spore and formation of young
gametophyte:
Under favourable conditions the spores germinate
immediately.
At the time of germination spore absorbs water and
swells up Exospore ruptures at the triradiate mark and
endospore comes out in the form of a tube. It is called
germ tube.
24. • Contents migrate into the germinal tube
where the colourless plastids turn green. Two
successive transverse walls are laid down at
the tip of a the germinal tube resulting in the
formation of three celled filament. The upper
cell divides by a vertical division followed by
similar vertical division in the lower cell
(quadrant stage).