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Read this essay to learn about the mechanism of pollination in some plants:- 1. Garden Sage 2. Garden Pea 3. Fig 4. Birthwort 5. Tape Grass 6. Swallow-Wort 7. Orchid.
Mechanism of Pollination in Some Plants
Essay Contents:
- Essay on the Mechanism of Pollination in Garden Sage (Salvia Plebeja)
- Essay on the Mechanism of Pollination in Garden Pea (Lathyrus Odoratus)
- Essay on the Mechanism of Pollination in Fig (Ficus Carica)
- Essay on the Mechanism of Pollination in Birthwort (Aristolochia Indica)
- Essay on the Mechanism of Pollination in Tape Grass (Vallisneria Spiralis)
- Essay on the Mechanism of Pollination in Swallow-Wort (Calotropis Gigantea)
- Essay on the Mechanism of Pollination in Orchid
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Essay # 1. Mechanism of Pollination in Garden Sage (Salvia Plebeja):
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The plant Salvia plebeja (Fig. 2.151) belongs to the family Lamiaceae (Labiatae) having bisexual flower with bilabiate corolla (with 2-lobed upper lip and 3-lobed lower lip). Two stamens are attached to the corolla tube and out of two anther lobes of each anther, one half is sterile and other one is fertile (Fig. 2.151 A,B).
The sterile halves of both the anthers jointly form a sterile plate of tissue which is placed above the lower lip near the mouth of the flower. The fertile anther lobe and the sterile anther knob are connected to one another by a curved connective.
The fertile anther lobes (one from each anther) are situated just under the upper corolla lobe. The lower lip of corolla forms a landing stage for the insects (bees). Nectarious fluid is secreted at the lower side of the hypogynous disc.
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As a bee comes and lands on the lower lip of flower and pushes in to collect nectar, it pushes the sterile plate; thereby the fertile anthers automatically come down and touch the backside of the bee, thus pollen grains are deposited in its backside (Fig. 2.151C).
The bee then flies away and goes to other flower to collect nectar again. If it goes to another flower in which the stigma hang down, backside of the bee is touched by the stigma and thus cross-pollination becomes effective.
Essay # 2. Mechanism of Pollination in Garden Pea (Lathyrus Odoratus):
The plant Lathyrus odoratus (Fig. 2.152) belongs to the subfamily Papilionoideae under the family Fabaceae, having papilionaceous corolla. The flowers are variously coloured and sweet-scented. The flowers are adapted for cross-pollination by insects, commonly by bee. The vexillum is the flag apparatus, the alae (wings) are the landing stage for the insects.
The flower is constructed in such a way that the weight of the bee on wings causes the keel (carina) to come down and thereby the hidden anthers and stigma are jerked out and come in contact with the body of the insect, where pollen becomes dusted. The bee then flies away and both the sex organs go back to their previous position.
When the bee visits another flower, some pollen from its body gets attached to the stigma and pollination occurs. The visitor bee may also receive fresh pollen from the second plant.
Essay # 3. Mechanism of Pollination in Fig (Ficus Carica):
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The plant Ficus carica (Fig. 2.153) belongs to the family Moraceae, having hypanthodium inflorescence. The flowers are adapted for cross-pollination by insect, the gall wasp (Blastophaga). There are three types of flowers: male, female (long-styled) and gall female (short-styled).
There is a narrow orifice at the top of the hypanthodium through which insects can enter. The male flowers are situated near the orifice, while long-styled female flowers and short-styled gall flowers are towards the base.
The gall wasp crawls into the receptacle and lays eggs inside the ovule of gall flowers. The eggs develop larvae which feed on ovule and form galls. The larva then develops into a mature wasp which comes out of the hypanthodium.
During coming out of the hypanthodium, the newly developed wasp brushes against male flowers and carries the pollen grains. When it visits another inflorescence, it pollinates the long-styled female flowers and lays egg within the gall flower.
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Essay # 4. Mechanism of Pollination in Birthwort (Aristolochia Indica):
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The plant Aristolochia indica (Fig. 2.154) belongs to the family Aristolochiaceae having flowers with a long perianth tube, swollen at the base. The swollen part encloses the sex organs. The inner side of the tube is slippery and with deflected hairs. The flowers are protogynous (i.e., gynoecium matures earlier than anthers).
Small insects (flies) are attracted by the foul odour and bright colour of the flowers. The deflected hairs allow the entry of the flies into the base, but prevent their escape. During its attempt to come out from the flower, it rubs against the stigma and thereby pollination is effected, if the fly carries pollen of other flower. Later on, the hairs wither, enabling the fly to escape.
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Essay # 5. Mechanism of Pollination in Tape Grass (Vallisneria Spiralis):
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In Vallisneria (Fig. 2.149), the flowers are borne under water. After maturation, the pistillate flowers are brought to the surface by their long stalk and form a cup-like depression.
The male flowers get detached from the male plant and float on the surface of water. If the male flower gets lodged into the depression, pollination occurs. After pollination, the elongated stalk of the pistillate flower undergoes spiral coiling, thereby it again goes under the water.
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Essay # 6. Mechanism of Pollination in Swallow-Wort (Calotropis Gigantea):
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The plant Calotropis gigantea Fig. 2.155) belongs to the family Asclepiadaceae; it shows an elaborate mechanism for cross-pollination by insects. In flowers, there are corona-like appendages which are associated with the secretion of nectar. Pollens are enclosed in pollinia.
The two pollinia of different anthers get attached to a common gland, the corpusculum or retinaculum (composed of glandular adhesive discs connected by translator), by two caudicles, situated at the corner of the 5-angled stigmatic head and remain covered by a membrane. In the mature flower, the membrane at the corners becomes slightly open.
When a bee visits a flower in quest of nectar, the corpusculum gets attached to the leg and the pollinia are pulled out forcibly if the bee moves away. When the bee visits another flower, these pollinia are deposited on the stigma. Thus cross-pollination is effected.
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Essay # 7. Mechanism of Pollination in Orchid:
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The orchids belong to the Family Orchidaceae. The highest level of adaptation for cross-pollination by insects is developed in orchid flowers (Fig. 2.156). The labellum (i.e., the posterior median member of the inner whorl of petal which is larger in size) acts as the flag and landing stage for the flies.
The rostellum (i.e., the sterile stigma) secretes a sticky fluid, by which the pollinia are adhered to the body of the insects. The gynostemium is formed (by the union of stamens and carpels) bearing two naked pollinia at its top, and below them lies the rostellum concealing the stigmatic surface (formed by the fusion of two fertile stigmas).
Usually the long-tongued bees come and land on labellum to get nectar concealed in the spur. During its attempt, the insect pushes back the rostellum and even breaks it. Thus the pollinia are released and get stuck to leg or forehead of insects by disc with the help of sticky fluid. At first, the pollinia stand erect, but due to flexible nature of caudicle they bend down during the movement of fly.
During visit of insect to other flower the pollinia get caught by the sticky fluid of the stigma and gradually the pollens are released. Thus the cross-pollination is effected.
