Chara (Stone- Wort)
Classification
Sub-division- Algae
Class- Chlorophyceae
Order- Charales
Family- Characeae
Genus- Chara
Practical work and study
Thallus
Study a slide showing a mounted part of thallus or Study a
preserved specimen.
1.Thallus is macroscopic, branched and multicellular. It
shows deposition of calcium carbonate all over.
2.It remains attached to the substratum by multicellular
rhizoids which bear an erect and branched main axis above.
3.Multicellular rhizoids are branched.
4.These are borne by the lower nodes of the main axis.
5.Rhizoids possess oblique septa. The rhizoids not
differentiated into nodes and internodes.
6.The cytoplasm of a rhizoidal cell has a nucleus situated
towards the upper side of the cell.
7. At the septum of a rhizoidal cell, the ends are
protracted in opposite directions to form knotted part.
8. At this place, signifying a node, a plate of four cells
or even more is formed which gives rise to rhizoidal branches. This part is
known as rhizoidal plate.
9. Main axis is composed of long internodes alternating with
small nodes.
10. Long internode is composed of a single cell enveloped by
many corticating threads.
11. A node is a group of regularly arranged cells.
12. It bears two types of branches—(i) lateral branches of
limited growth (short laterals) and (ii) lateral branches of unlimited growth
(long laterals).
13. Laterals of limited growth are borne in whorls around
the nodes of the main axis.
14. Each short lateral is divided into nodes and internodes.
15. The internodes of short laterals are small as compared
to those of the main axis.
16. Short laterals borne by the nodes of the main axis are
also termed as primary laterals of limited growth.
17. From the nodes of the short laterals, secondary short
laterals are produced which are usually small, unicellular and are variously
termed as stipules or leaves.
18. Laterals of unlimited growth are borne by the nodes of
the main axis only. These are situated in the axils of short laterals.
19. Long laterals possess the same characteristics as those
of the main axis.
20. Long laterals are differentiated into long, corticated
and unicellular internodes and small and multicellular nodes.
21. Nodes of the long laterals bear short laterals which in
their turn give out stipules or leaves at their nodes.
A cell
Study the slide showing T.s. of internodal cell.
1. In the centre is a large central, axial or internodal
cell.
2. lt is surrounded by corticating threads on all sides.
3. Internodal cell shows a typical cell structure.
4. Centre of the cell has a big vacuole surrounded by
cytoplasm.
5. In the cytoplasm lies a single nucleus held by thin and
delicate cytoplasmic strands.
6. Many discoid chloroplasts without pyrenoids are scattered
in the peripheral cytoplasm.
7. The cell has an outermost, thick and firm cell wall.
Apex
Study the slide showing L.s. of apex.
1. The cell situated at the top is an apical cell. It
contributes to the development of the main axis and lateral axes.
2. It cuts off a longitudinal series of cells below it.
3. Upper biconcave cell of a series is a nodal cell and
lower biconvex one is an internodal cell.
4. Biconcave nodal cell in the lower farts divides to
produce a mass of peripheral cells which surrounds centrally located nodal
cell.
5. Peripheral cells act as initials of the laterals of
limited growth.
6. From peripheral cells of node, laterals are produced
which show similar arrangement of nodal and internodal cells alternating with
one another.
7. Biconvex internodal cell does not divide but in the lower
part simply elongates many times.
Bulbils
Study a slide of a thallus bearing bulbils.
1. Bulbils are present on the knotted part of the rhizoid or
the basal nodes of the main axis.
2. These remain buried under the soil.
3. These are oval, tuber-like outgrowths.
4. Bulbils are rich in starch and hence also called amylum
stars.
5. These are the organs of vegetative propagation.
Sex organs
Study a slide or a part of thallus bearing sex organs.
1. Most of the species are homothallic (monoecious) while a
few are heterothallic (dioecious).
2. The male reproductive organ is called a ‘globule’ while
the female reproductive organ a ‘nucule’.
3. Both the sex organs are borne at one point on the nodes
of short laterals which bear stipules.
4. The characteristic feature ‘of the genus Chara is the position of nucule at the node above the globule.
Male sex organ
Study the external features of globule, then press it a little to observe internal structure.
Also pierce through it by a needle to separate the shield cells and associated structures. Slide of L.s. of globule would also show almost the same structure.
1. A globule is a small, spherical and conspicuously red or yellow structure attached to the node by a long stalk cell.
2. Outermost wall of the globule is ornamented, composed of
eight, large, curved and plate-like cells, shield cells.
3. Ornamentation of the shield cell is due to the foldings
in the cell wall.
4. Each shield cell is attached to a long handle or a
rod-shaped cell-manubrium.
5. At the tip of each manubrium are two groups of six cells
each. The group directly in contact with the manubrium is primary capitulum
while the next is secondary capitulum.
6. Each secondary capitulum bears 2-4, long and unbranched
antheridial filaments.
7. Each antheridial filament is composed of 100-230 small cells.
8. Each of these cells is an antheridium and produces a
single biflagellate male gamete.
Female sex organ
Study the whole mounts of nucule and a zygote.
1. Nucule is oval in shape and is situated above the globule
at the node.
2. It is enveloped by spirally coiled (coiling clockwise)
cells—tube cells.
3. At the apex of the nucule is a corona of five small cells arranged in one tier and attached at One point.
4. Oosphere is single celled where a nucleus lies surrounded
by the cytoplasm.
5. It is rich in food reserves which are in the form of
starch and oil.
6. After fertilization the nucule gets modified into a
zygote or oospore.
7. The coronal cells at the top of the oospore appear
separated.
8. The oospore wall is thick and ornamented. It has a deposition of calcium.
Reproduction in Chara:
Reproduction in Chara takes place by vegetative and sexual
methods. Asexual reproduction is absent.
(i) Vegetative Reproduction in Chara:
Vegetative reproduction in Chara takes place by following
methods:
(a) Bulbils:
The bulbils are spherical or oval tube-like structures which develop on rhizoids t . C. aspora or on lower nodes of main axis e.g., C. baltica. The bulbils on detachment from plants germinate into new thallus (Fig.)
In some species of Chara e.g., C. stelligna, on the lower nodes of main axis develop multicellular star shape aggregates of cells (Fig. 6 B). These cells are full of amylum starch and hence are called Amylum stars. The amylum stars do detachment from plants develops into new Chara thalli.
(c) Amorphous bulbils:
The amoiphous bulbils are group, many cells, irregular in
shape which develop on lower node main axis e.g., C. delicatula or on rhizoids e.g.,
C. fragifera and C. baltica. The amorphous bulbils are perennating structures,
when the main plant dies under unfavorable conditions; these bulbils survive
and make Chara plants on return of favourable conditions.
(d) Secondary Protonema:
These are tubular or filamentous structure which develops from primary protonema or the basal cells of the rhizoids. The secondary protonema like primary protonema form Chara plants.
(ii) Sexual Reproduction in Chara:
The sexual reproduction in Chara is of highly advanced oogamous type. The sex organs are macroscopic and complex in organization.
The male sex organs are called antheridium or globule and the female oogonium or nucule. Most of the Chara species are homothallic i.e., the male and male sex organs are borne on the same nodes, (Fig.) e.g., C. zeylanica. Some species e.g., C. wallichii are heterothallic i.e., male and female sex organs are borne on different plants.
The sex organs arise on the branches of limited growth or primary laterals, the nucule above the globule. The development of globule and nucule takes place simultaneously but species globule matures before nucule
Life Cycle of Chara:
The plant body of Chara is haploid. The vegetative reproduction takes place by the formation of amylum stars, bulbils and secondary protonema. Asexual reproduction is absent. The sexual reproduction is advanced oogamous type.
The male and female sex organs are globule and nucule respectively. After fertilization a diploid spore is formed. At the time of germination diploid oospore nucleus divides to make hapoid nuclei and haploid Chara plant. Thus the life cycle of Chara a predominantly haploid type.
Identification
Sub-division—Algae.
(1) Simple construction of thallus,
(2) Presence of chlorophyll,
(3) Cell wall of cellulose.
Class—Chlorophyceae.
(1) Chloroplasts grass-green in colour,
(2) Photosynthetic reserve-starch,
(3) Motile reproductive bodies flagellated,
(4) Flagella equal in length.
Order—Charales,
(1) Thallus differentiated into nodes and internodes,
(2) Characteristic sex organs—globule and nucule.
Family—Characeae, Single family.
Genus—Chara
(1) Presence of corticating filaments around internodes,
(2) Nucule lying above the globule.
(3) Corona of nucule five celled.
Hints for collection
It is. aquatic in habitat. It grows in fresh, clear and standing waters on a muddy or a sandy bottom (epipelic community). These form extensive sub-aquatic growth. The genus is found below the water level, growing to a considerable depth. It can be collected, almost from any standing or stagnant reservoir of water and occurs in fruiting state during early and late winters. Many species become encrusted with calcium carbonate and are rough and brittle. Chara owes its name ‘Stone-worts’ to this character.