In this article we will discuss about the anatomy of sargassum.
Insert the material (axis, leaf, air bladder) in pith, cut its transverse sections, stain in safranin, wash with water, mount in glycerine and study under microscope.
T.S. Axis:
1. Axis is differentiated into meristoderm, cortex and medulla (Fig. 40).
2. Meristoderm is the outermost layer made up of closely-packed, small cells. The cells aremeristematic in nature and filled with chromatophores. It is also covered by a layer of cuticle. This layer is also known as epidermis, and due to the presence of chromatophores its function is photosynthetic.
3. Below the meristoderm is the region of cortex. It is made up of many parenchymatous cells. Cells are polygonal in shape and bear intercellular spaces. Cells are filled with reserve food, and so it is also known as storage tissue.
4. Centre of the axis is occupied by a thick-walled region or medulla.
5. Cells of the medulla are narrow and elongated.
6. Lateral walls of medulla bear some scalariform thickenings.
7. Conduction of water and other nutrients is supposed to be the function of medulla.
T.S. Leaf:
1. All the structures in “leaf’ are essentially similar to that of axis, i.e., it is also divided into epidermis, cortex and medulla (Fig. 41).
2.”Leaf’ is more thick in the midrib region, and the wings are narrow, long and thin (Fig. 41).
3. Epidermis is made up of small cells having chromatophores. Cortex is mainly distributed in wings with few cells thick in midrib region.
4. Medulla is present only in the midrib region.
5. Many flask-shaped cryptostomata or sterile conceptacles are also present in the “leaf”. They contain many sterile hairs or paraphyses.
6. Cryptostomata open by a pore known as ostiole.
7. Epidermis is photosynthetic in function, cortex acts as storage region, and medulla serves the function of conduction. Thus, there is a division of labour in tissues in Sargassum.
T.S. Air Bladder:
It shows the following structures (Fig. 42).
1. The outermost layer is meristoderm.
2. Inner to the meristoderm is present many-celled thick parenchymatous cortex.
3. In the centre of the air bladder is present a hollow cavity filled with air and gases.
4. Air bladders help in floatation.
Reproduction:
1. Asexual reproduction is absent.
2 Sexual reproduction is oogamous. Male and female sex organs are known as antheridia and oogonia, respectively.
3. Sex organs are present in flask-shaped fertile conceptacles, restricted only in specialized branches called receptacles.
4. Plants are monoecious but a few species are dioceious. In monoecious plants also, the male and female sex organs are generally present in different .conceptacles. So, conceptacles are generally unisexual.
T.S. Receptacular Branch:
1. Receptacle contains many flask-shaped fertile conceptacles.
2. Each conceptacle is in the form of a cavity opening outside by an ostiole.
3. Cells of conceptacle wall are filled with many chromatophores.
4. Wall of the conceptacle gives rise to many multicellular, branched or unbranched, hair-like paraphyses.
5. Each conceptacle contains either antheridia or oogonia, and known as male or female conceptacle, respectively.
T.S. Through Male Conceptacle:
1. In the male conceptacle are present many antheridia (Fig. 44A).
2. Each antheridium is a small, ovoid and stalked structure present generally on lower branches of paraphyses.
3. Many antheridia are present on a paraphysis (Fig. 44B).
4. Each antheridium contains many antherozoids.
5. Each antherozoid is unicellular, uninucleate and pear- shaped structure, with two laterally attached flagella.
T.S. Through Female Conceptacle:
1. In structure, female conceptacles are the same flask- shaped cavities having many paraphyses, and opening by an ostiole (Fig. 45).
2. Many oogonia (Fig. 45) are present in the female conceptacle.
3. Each oogonium is rounded, and sessile when young, but contains long gelatinous stalk at maturity.
4. Oogonium remains surrounded by three-layered wall, i.e., exochite, mesochite and endochite.
5. Each oogonium contains a single uninucleate egg (Fig. 46).
6. Fertilization is internal and zygote germinates without any resting period.
