Full size table The total assembly length varied between and Mb, which is consistent with the size estimates based on k-mer analysis Table 1 but slightly larger than those from flow cytometry 17 , The genome size variation among the three strains can be largely attributed to the differences in repeat content Supplementary Fig. A combination of ab initio, evidence-based and comparative gene prediction approaches resulted in 24,—25, predicted protein-coding genes Supplementary Table 5. For A. The three hornwort genomes show a high gene density compared to other land plants Supplementary Table 6.

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They are present in shady places or ;n the crevices of rocks. Anthoceros erecrus, A. 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. Mucilage oozes out through these slits. Internal Structure of the thallus 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.

Fig: Internal structure of Thallus Growth of thallus 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. Reproduction Vegetative Reproduction 1. Death of older pans: Vegetative reproduction takes place by the death of older parts. Younger parts form new thallus. Tuber: 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: Gemmae are also produced on short stalks on the upper surface of the thallus. These are also act as vegetative reproductive bodies.

Sexual Reproduction 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. Antheridia 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 rnulticellular 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 Development of Antheridium I. 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 muci I ge. 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. 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 fcur cells. Periclinal divisions take place in all these cells. It produces central androgonial cells and peripheral jacket cells. The jacket. 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 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. Development of Archegonium 1. 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 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. Sporophyte or Sporogonium: The sporophyte of Anthoceros has certain unique features. Sporogonium is borne on the gametophyte. But mature sporogonium does not totally dependent on the gametophyte. Foot: A mature sporogonium has a well developed cup-like foot. This foot has few rhizoids at the base. Capsule: Capsule forms the upper part of the sporogonium. It is long, narrow and cylindrical.

It has no distinct seta.


Reproduction in Anthoceros (With Diagram)

They are present in shady places or ;n the crevices of rocks. Anthoceros erecrus, A. It is lobed and it has irregular or dichotomous branches. The lobes have a wavy margin.



Gametophytic Phase of Anthoceros: i External Features: The gametophytic plant body is thalloid, dorsiventral, prostrate, dark green in colour with a tendency towards dichotomous branching. Such branching results into an orbicular or semi orbicular rosette like appearance of the thallus. The thallus is bilobed A. Dorsal Surface: The dorsal surface of the thallus may be smooth A. It is shining, thick in the middle and without a distinct mid rib Fig.


Type Anthoceros – Structure, Reproduction and Development

They are present in shady places or in the crevices of rocks. Anthoceros erecrus, A. General structure 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.

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