Anthoceros ppt. 5, views ORDER: Anthocerotales • FAMILY: Anthocerotaceae • GENUS: Anthoceros; 2. SCHEMATIC LIFE CYCLE; Anthoceros is a genus of hornworts in the family Anthocerotaceae. The genus is global in its distribution. Its name means ‘flower horn’, and refers to the. became apparent that numerous features of the life-cycle had been either The genus Anthoceros was established by Micheli in , that is to say.
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Anthoceros grows on moist soil. They are present in shady places or in the crevices of rocks. Anthoceros has thallus body. It is lobed and it has irregular or dichotomous branches. The lobes have a wavy margin. Anthoceros form small rosette like plant. Unicellular rhizoids are attached to the underside of the thallus. Small mucilaginous cavities are present on the ventral side. These cavities contain colonies of a blue green alga like Nostoc.
Stomata like small slits are present on the dorsal side of the thallus. Mucilage oozes out through these slits. The thallus has uniform tissue of parenchymatous cells. Epidermis is present on both sides. The cells in the upper region contain the chloroplasts. Generally each cell contains a single chloroplast. Each chloroplast has a pyrenoid. The thallus is thickest in the middle. It gradually becomes thinner towards the margins. Cells of the lower epidermis give rise to smooth unicellular rhizoids.
The growth occurs by single apical cell in initial stages. But mature plants have several scattered apical cells on the margin. So growth takes place at many points. It forms rosette like thallus. Death of older parts: Vegetative reproduction takes place by the death of older parts.
Younger parts form new thallus.
Establishment of Anthoceros agrestis as a model species for studying the biology of hornworts
Some thallus forms tubers. These tubers are rich in stored fats and proteins. These tubers germinate to on the margin of the lobes. They can survive long periods of drought.
Tuber detach and from new plants. Gemmae are also produced on short stalks on the upper surface of the thallus. These are also act as vegetative reproductive bodies.
Anthoceros has both monoecious and dioecious species.
Male plants are smaller than the female in the dioecious species. In monoecious species the antheridia are produced earlier than archegonia. The sex organs are deeply embedded in the thallus.
The antheridia are present on the upper side of the thallus in small cavities. They are found in groups of The antheridial cavities are completely covered by a double layer of cells.
They have no opening to the outside. Each antheridium is borne on a multicellular stalk. The main body of the antheridium is globose.
It has a single celled thick jacket. Antheridia have mass of androgonial cells. They give rise to biflagellate antherozoids. Antheridium develops from a single superficial cell of the thallus. This cell divides by a transverse division into an outer and an inner cell.
The inner cell acts as antheridial initial. A space is produced between inner and outer cells. This space is filled by mucilage.
The inner cell is pushed towards the base of cavity. The outer cell divides to form roof of antheridial cavity. The antheridial initial divides by one or two vertical divisions.
It produces two or four cells. Each of which develops into an antheridium. Thus it gives rise to a group of antheridia in each cavity.
Reproduction in Anthoceros (With Diagram)
Each antheridial cell divides by transverse division. It produces a primary stalk cell at the base and a primary antheridial cell at the top. The primary stalk cell divides to from multicellular stalk. The primary antheridial cell first divides by two vertical divisions at right angle to each other. It produces a group of four cells. One or more transverse divisions take place. It produces tiers of four cells. Periclinal divisions take place in all these cells.
It produces central androgonial cells and peripheral jacket cells. The jacket cells by further divisions produce a single layered wall. The androgonial cells produce a mass of androcytes or antherozoid mother cells. The contents of each antherozoid mother cell are transformed into a single antherozoid.
The roof of the antheridial cavity and antheridial wall ruptures. It releases antherozoids in the surrounding water. Archegonia are produced close to the growing point. Archegonia are embedded in the tissue of the thallus. Each archegonium consists of an egg and a ventral canal cell four neck canal cells.
The canal of the archegonium is closed at the top by four cover cells. These cells project slightly above the general surface of the thallus.
Studies on the Morphology of Anthoceros. I1 | Annals of Botany | Oxford Academic
Each archegonium develops from a single superficial cell of the thallus. The archegonial initial divides by three vertical divisions. It produces a large axial cell and three peripheral jacket initials. The axial cell divides transversely. It cuts off a small cover cell at the top.
It divides into a lower primary ventral cell and an upper primary canal cell. The primary ventral cell divides transversely. It produces a larger egg or oosphere at the base and a small ventral canal cell at the top.
The primary canal cell divides transversely to produce t. The cover cell divides vertically twice to produce four cover cells. The neck canal cells and vennal canal cells produces a mass of mucilage at maturity.
It forms an opening for the release of antherozoids. The plant becomes wet with dew or rain during fertilization. The antherozoids are attracted towards the archegonium chemotactically. Antherozoids enter the archegonium through the neck canal. One of them fuses with the egg to complete the fertilization. The zygote increases in size and completely fills the venter. It secretes a wall to become the oospore. The sporophyte of Anthoceros has certain unique features.
Sporogonium is borne on the gametophyte. A mature sporogonium has a well developed cup-like foot. This foot has few rhizoids at the base. Capsule forms the upper part of the sporogonium.