LIFE CYCLE OF MARSILEA PDF

Samuzuru The sporangium wall of Marsilea shows no sign of cellular specialisation e. Each lateral vein divides dichotomously about middle of its base and the apex. All the four segments divide by anticlinal divisions several times giving rise to a one-celled thick vegetative tissue. The shape of pinna varies from obovate to obcuneate and margin also varies from entire to crenate or crenate to lobed.

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Habit and Habitat of Marsilea 2. External Features of Marsilea 3. Internal Structure 4. Reproduction 5. Life Cycle Patterns. It is represented by about 53 species which are cosmopolitan in distribution but abundantly found in tropical countries like Africa and Australia. About 9 species have been reported from India. Either the species are hydrophytic or amphibious i. External Features of Marsilea: The mature sporophyte is an herbaceous plant.

Its underground rhizome spreads in a diameter of 25 meter or more. The plant body is distinctly differentiated into rhizome, leaves and roots Fig. Rhizome: All the species possess a rhizome which creeps on or just beneath the soil surface. It is slender, dichotomously branched with distinct nodes and internodes and is capable of indefinite growth in all directions as a result of which it occupies an area of 25 metre or more in diameter.

In aquatic species the internodes are long while in sub-terrestrial species they are short. Usually from the upper side at nodes, the leaves are given out while from their lower side, the roots. Leaves: They are borne alternately on upper side of rhizome at nodes, in two rows. Young leaves show circinate vernation like ferns Fig.

In some species young leaves are covered with multicellular hairs. The leaves are compound, with basal petiole and terminal lamina. In submerged plants the petiole is a long and flexible structure and the lamina floats over the surface of water but in muddy or marshy plants the petiole of the leaf is short and rigid with short lamina spreading in the air.

The lamina consists of 4 leaflets pinnae which are present at the apex of petiole. The 4 leaflets arise as a result of 3 dichotomies of the lamina in close succession to each other i.

Puri and Garg suggested that the leaf consists of single pinna consisting of 4 pinnules. Pinnae have got a dichotomously branched vein system with cross connections Fig. The veinlets at the margin are connected with loops thus forming a reticulum. The shape of pinna varies from obovate to obcuneate and margin also varies from entire to crenate or crenate to lobed. Sometimes the pinnas are once or twice deeply dichotomously lobed M. At night the pinna are folded upwardly. This is known as sleeping movement of pinna.

Near the base of petiole the stalked bean-shaped sporocarps are borne. In certain cases the roots are given out even from the internodes M. Internal Structure of Marsilea: 1. Rhizome stem : A T. The stomata are absent. It is parenchymatous and may be one to several cells thick. Some of its cells contain tannin. It lies below the hypodermis.

It consists of large air spaces chambers separated by one cell thick parenchymatous septa. In the xerophytic species e. The outer layers are thick walled sclerenchymatous while the inner layer of cells is thin walled parenchymatous and compactly arranged. Some of these cells are filled with starch or tannin. Xylem is present in the form of a complete ring which is surrounded on both sides by a complete ring of inner and outer phloem, pericycle and endodermis. In this way the continuation of different tissues in the form of complete ring in stele is as follows—outer endodermis, outer pericycle, outer phloem, xylem, inner phloem, inner pericycle and inner endodermis.

The protoxylem may be well defined exarch M. The cells are parenchymatous and slightly elongated. It is made of thin walled cells parenchymatous. It consists a ring of air chambers. The air chambers are separated by single layered partitions of thin-walled parenchymatous cells. The cell layers are parenchymatous and contain starch and tannin filled cells. Each arm is provided with metaxylem elements in the centre and protoxylem is situated at both the margins i.

The xylem is surrounded on all sides by phloem. Phloem is externally surrounded by a single layer of parenchymatouspericycle which, in turn, is bounded by a single layered endodermis. Transverse Section of Leaflet: A. It is differentiated into upper and lower epidermis. In floating leaflets the stomata are present on the upper epidermis but in case of plants growing in mud or moist soil where the leaves are aerial, the stomata are present both on upper as well as lower epidermis.

It is usually differentiated into an upper palisade tissue and lower spongy parenchyma. The palisade tissue is made up of elongated cells provided with chloroplast. The spongy tissue is made up of loosely arranged parenchymatous cells with large air spaces separated by single layered septa. In submerged species, however, the mesophyll is not differentiated into palisade and spongy parenchyma. Each vascular bundle is concentric and amphicribal type i.

The phloem is enclosed by a single layered thick endodermis. Root: A T. The outer cortex consists of large air chambers arranged in the form of a ring parenchymatous. These chambers are separated from each other by longitudinal septa.

The inner cortex is differentiated into outer parenchymatous and inner sclerenchymatous regions. The inner cortex is delimited by single layered thick endodermis. It is devoid of pith. Xylem is situated in the centre which is diarch and exarch. It is surrounded by phloem. The phloem is bounded externally by a single layer of pericycle.

Reproduction in Marsilea: Marsilea reproduces by two methods: i Vegetative reproduction ii Sexual reproduction. Vegetative reproduction: It takes place by means of tubers which are produced in dry conditions from the rhizome. First a branch is given out from the rhizome, which later on swells up due to the accumulation of food material.

The structure is termed as tuber and is capable of tiding over the unfavourable conditions. On the return of favourable conditions it germinates to produce a new sporophytic plant, e. Sporophytic Phase: Spore producing organs: Marsilea is heterosporous i.

These spores are produced in microsporangia and megasporangia, respectively. These sporangia are borne in special type of spore producing organ called sporocarp. The sporocarp are born laterally on the short and lateral branches of the called the peduncles or pedials petiole of leaf either near the base or a little higher up. They arise solitary or in clusters. The peduncle is usually unbranched but it may be branched also.

Number of sporocarp differs in different species and varies from 1 to 20 or more. The attachment of the pedicel sporocarp varies in different species. Mainly it is of three types Gupta : i Pedicel of the solitary sporocarp is directly attached to the base of the petiole e. External Morphology of Sporocarp: Each sporocarp is an oval or bean shaped biconvex, flattened structure. It is green and soft when it is young but at maturity it becomes very hard and brown in colour.

It is made up of a short stalk like structure known as peduncle and the body. The point of attachment of peduncle with the body is called raphe Fig. Slightly above the raphe in a median plane are present 1 or 2 protuberances called tubercles.

They are unequal in size and lower one is stouter than the upper one. In some cases the tubercles are absent e. Internal Structure of Mature Sporocarp: The sporocarp is a bivalved structure. It can be split open in the dorsiventral plane into two halves valves. If we split open the sporocarp, we can see the following structures: Wall of sporocarp: It is very hard, thick and highly resistant to mechanical injury. It can be differentiated into three zones—outer epidermis, middle hypodermis and inner parenchymatous zone.

Epidermis is single layered made up of broad and columnar cells. Its continuity is broken by the presence of sunken stomata Fig. Some of the epidermal cells develop into multicellular hairs Fig.

Hypodermis consists of two layers of radially elongated palisade like cells.

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Marsileaceae Genus. There are about 65 species of Marsilea distributed all over the world. They are more commonly found in tropical regions, such as, Africa and Australia. Gupta and Bhardwaja have recorded about ten species of Marsilea from our country. About six species of Marsilea are known to occur in the United States.

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