3. AN OVERVIEW
● HABIT
● MORPHOLOGY
● ANATOMY
● REPRODUCTION
● THE SPOROPHYTE
● DEHISCENCE OF
CAPSULE
● NEW GAMETOPHYTE
4. HABIT
Pogonatum is a genus of mosses —
commonly called spike moss — which
contains approximately 70 species that cover
a cosmopolitan distribution.
● It can be seen mostly in Asian countries
with a tropical climate.
5. Morphology
● The gametophyte is perennial,
differentiates into a rhizomatous
basal portion and aerial upright
shoots (Fig. 6.54A).
● The basal portion bears numerous
rhizoids.
● The rhizoids are multicellular,
elongated, thick-walled with oblique
septa and are twisted together in a
rope-like manner to form strong
cable-like strings.
6. ● The aerial shoot may be unbranched
or branched, composed of a central
axis, covered with spirally arranged
leaves.
● In the lower part of the upright
stem, the leaves are very small,
scaly and much paler in colour.
● While, in the upper part of the stem,
the leaves are comparatively larger
with broad sheathing bases.
● The upper part of these large
leaves extend into a narrow
brown or deep red coloured
limb having serrated margins.
● The leaves are provided with a
thick midrib and two laterally
extended thin and narrow
wing-like lamina.
7. Anatomy
Stem
A T.S. of the stem shows an epidermis, the
cortex and the central cylinder consisting of
elongated leptoids and hadrom cylinder .
● The epidermis is the outermost covering
of the stem, composed of thick- walled
cells.
● The epidermis is broken up giving an
irregular outline of the stem by the
interruption of a number of leaf bases.
8. The cortex is differentiated into two
zones, the outer cortex and the inner
cortex.
● The outer cortex is composed of
deeply coloured, 3-5 layered
chlorenchymatous cells.
● The inner cortex is made up of
thin-walled parenchymatous cells,
full of starch.
9. Many leaf-traces are present in the outer
part of the inner cortex, comprising of a
small group of thick-walled cells.
● Next to cortex, a zone called leptoid is
present which is comprised of
elongated living cells, devoid of starch.
● This zone is comparable to the sieve
tubes of the higher plants.
● There is a zone of leptoid cells
interspersed with starch-containing
cells, called leptoid mantle.
10. The central zone of the stem is called
hadrom cylinder, comprised of two
types of cells:
● the elongated thick- walled cells
with protoplasts, called stereides,
● and thin-walled cells, devoid of
protoplasts, called hydroids.
11. Leaf
● The upper surface of the midrib is
completely covered by parallel
vertical plates of cells, called
lamellae .
● This is comparable to the gills of
Agaricus fungi.
● Each lamella consists of 4-8 cells .
● All the cells, except the terminal one
contain chloroplasts.
12. ● The terminal cell is larger than the
remaining cells of the lamellae.
● In some species (viz. P.
microstromium), terminal cells split
into two conical cells. The lower
epidermis forms a distinct layer,
comprised of thin-walled cells.
13. Reproduction
Vegetative propagation
Vegetative propagation of Pogonatum
takes place by the following methods:
● Gemmae:
● Secondary Protonema:
Gemmae
Bud-like gemmae develop on the
rope-like rhizoids and each gemma forms
a gametophyte after germination.
14. Secondary Protonema:
● The secondary protonema develops from any part of the plant
other than spores.
● Many buds are produced on the protonema which are capable
of growing into new plants.
● Sometimes, a diploid protonema is produced aposporously
from the tissue of sporophyte without the formation of spores,
thus giving rise to a diploid gametophyte.
15. Sexual Reproduction
Pogonatum is usually dioecious i.e., hetero-
thallic, although a few monoecious species
(P. microstromium) have been reported.
The development of sex organs in
Pogonatum is similar to that of Funaria.
16. Antheridial Head:
● Antheridia are borne at the apex of the male
shoot.
● They are surrounded by the perichaetial
leaves which are red or orange in colour .
● The antheridial head forms a compound
cluster cup structure or inflorescence.
● At the base of each perichaetial leaf,
clusters of antheridia and hairs like
multicellular paraphyses are present .
17. Antheridium:
● The development of antheridium in
Pogonatum is similar to that of Funaria.
● The mature antheridium is made up of a
club-shaped body and a short multicellular
stalk .
● The body has a single-layered jacket
surrounding a central mass of androcyte
mother cells.
● Each androcyte mother cell divides
mitotically to form two androcytes and
each androcyte is metamorphosed into a
curved biflagellate antherozoid or sperm .
18. Archegonial Head:
● Archegonia also develop in
clusters of 3-6 at the top of the
female shoot .
● They are also surrounded by
paraphyses and perichaetial
leaves.
19. Archegonium:
● The development of archegonia in Pogonatum is similar to that of Funaria.
● The mature archegonium is a shortly stalked flask-shaped body, differentiates
into a massive venter and a long neck .
● The archegonial jacket is single-layered in neck region, while it is multilayered
in venter region. The neck consists of six vertical rows of neck cells and 6-9
neck canal cells. The venter contains a ventral canal cell and a large egg or
oosphere.
20. Fertilisation of Archegonium:
● The fertilisation process in Pogonatum is like that of other mosses.
● At the top of the archegonia a clear passage is formed due to the dissolution of
neck canal cells and ventral canal cell. Like other bryophytes, water is essential
for free swimming of sperms towards the neck of the archegonium.
● Finally, one antherozoid fuses with the egg to form a diploid zygote or oospore,
thus the sporophytic generation begins. More than one archegonia may be
fertilised, but usually one sporophyte is matured in the archegonial branch.
22. Structure of the Mature Sporophyte:
The mature sporophyte of Pogonatum is differentiated into
a foot, a long seta and a capsule .
1. Foot:
It is a dagger-shaped structure, penetrating the tip of the
gametophyte. The foot is made up of thin-walled
parenchymatous cells.
2. Seta:
It is green in colour when young and becomes reddish to
deep-brown at maturity. Anatomically, it is differentiated
into an epidermis of one layer, hypodermis of several layers
of thick-walled cells, a cortex of loosely arranged
parenchymatous cells and a central cylinder of very
thin-walled cells .
23. 3. Capsule:
The capsule is differentiated into the following three parts:
(a) Opercular Region:
It is a conical apical part of the capsule which is a beaked
cup-like structure . It is connected with the theca by a ring-like
diaphragm, but there is no organised annulus.
(b) Theca:
It is the middle part of the capsule. It is urn-shaped fertile
part of the capsule which appears oval or elliptical in
outline when viewed in a transverse section. The jacket or
wall of the theca is 4-5 layered thick. The outermost layer
is the epidermis which is devoid of stomata.
24. (c) Apophysis:
It is the basal part of the capsule, mostly
comprised of parenchymatous cells. It has a
thick-walled epidermis. The central part is
occupied by the conducting strand which is
in continuity with the columella and seta.
25. Dehiscence of Capsule:
● At maturity, the capsule dries up, the calyptra
falls off and the operculum is broken loose by the
pressure of the columella.
● Subsequently, the operculum drops off exposing
the peristome teeth.
● The cells near the peristome teeth breaks forming
minute hole.
● The spores are released through the minute holes
that are controlled by the upward and downward
movement of the peristome teeth.
26. New Gametophyte
● The spore is the first cell of the
gametophytic generation.
● The spores are small and spherical.
● The spore wall is differentiated into an
outer smooth-walled exine and an
inner delicate intine.
● The spores contain a considerable
amount of chloroplasts and oil bodies
in their cytoplasm.
27. ● The spore germinates under favourable conditions.
● The exine ruptures and the intine comes out in the form of one or more green algal
filament. The filament cuts off cells, becomes septate and forms filamentous primary
protonema. The protonema branches freely by means of an apical cell and subsequently,
forms two types of branches, viz. chloronemal branches and rhizoidal branches .
● The non-green rhizoidal branches develop below the substratum and are meant for
anchoring the protonema in the substratum. The chloronemal branches are green and
aerial being rich in chloroplasts and bear many lateral buds. Each bud grows into an
adult leafy gametophore.
