Pollination by Water: Definition, Types and Characteristics

Ans. Pollination is a process in which the pollen grain is shed from the anther and reaches the stigma of a pistil. This process takes place within the same flower, same plant, and different plants with the help of abiotic and biotic agents.

There are three agents that facilitate pollination in plants:

• Wind Pollination - It is an abiotic agent in which the pollen grains travel from the anther to the stigma through the flowing wind. 
• Water Pollination - It is an abiotic agent in which the pollen grains travel from another to the stigma with the help of a water current.
• Pollination through animals - Animals and insects are the biotic agents. The anther sticks to the body of the animals and insects and reaches the stigma of the pistil.

Ans. When the pollen grains are released either on the surface of the water or underwater and get drifted by the water current and come in contact with the stigma, then it is called pollination by water. Water Pollination is of two types:

• Hypohydrophily - When the pollen grains are released below the surface of the water then they sink down and get caught by the stigma of the female flower. then they are called hypohydrophily. An example of hypohydrophily is seagrass.
• Epihydrophily - When the pollen grains float on the surface of the water and reach the stigma of the female flower, then it is called Epihydrophily. An example of this pollination is Vallisneria.

Ans. There are many aquatic plants that prefer air and animals for pollination. Water pollination is a rare method and there are very few plants that pollinate through the water. Some of the aquatic plants that use water for pollination include Hydrilla, Vallisneria, and Zostera (Seagrass).

Ans. Vallisneria is an aquatic plant that uses water for cross-pollination. The stalk of the female flower reaches the surface of the water and the male flower or the pollen grains are released on the surface. These pollen grains are then carried away by the water current and reach the stigma of the flower.

Water lilies are also aquatic plants but they pollinate with the help of wind or insects. Water lilies have large flowers on the surface of the water. It attracts insects by offering nectar. The insects sit on the flowers and the pollen grains stick to the insect's body. When the insects sit on the female flower then pollination occurs.

Ans. Some of the features that the water pollinated plants possess are:

• Water pollinated plants are usually aquatic.
• They produce a large number of pollen grains as most of them get lost in the water flow and very few are able to reach the stigma.
• The stigmas of the female flower are usually above the water and are large and feathery to catch the pollen grains.
• The male flowers release the pollen grains that differ for both underwater and surface water pollen grains. The surface pollens are lighter and the underwater pollens are heavier than water.
• The male flower after maturation detaches itself from the plant and floats above the water surface.

Ans. Vallisneria is a genus of aquatic plants. In this plant, pollination is done by pollinating agents i.e., water. Female flowers have long stalked and appear on the surface of the water. When the male flower releases pollen grain it reaches the stigma of the female flower through a water current.

Ans. Water-mediated pollination takes place in selected plants like Vallisneria. In this plant, the female flower reaches the surface of the water. Pollen grains get sprinkled on the water surface and are passively transported to the female flower for pollination. In seagrasses, the female flower stays submerged in water and pollen grains are released below the water surface. In pollination by water, pollen grains have a mucilaginous covering that protects the pollens from getting wet.

Ans. The pollinating agent in the described inflorescence with small dull-colored flowers having well-exposed stamens and large stigma is wind. The pollens are non-sticky and can be easily dispersed by wind currents and so a large, feathery stigma easily traps air-borne pollen grain. 

Example: Corn cob, its ears, or silk (stigma and style) wave in the wind to trap pollen grains.

Ans. Emasculation is a bisexual flower helps to prevent contamination of stigma with self-pollen grains. Bagging prevents contamination of the stigma of the emasculated flower with any other unwanted pollen grains. Thus, a bisexual flower should be emasculated and bagged prior to artificial pollination.

Ans. The three outbreeding devices that flowering plants have developed, so as to encourage cross-pollination are:

(i)Receptivity of stigma and release of the pollen grain is not synchronized, i.e. stigma becomes receptive much before pollens are released or after they are released to avoid self-pollination.

(ii) Self-incompatibility, a genetic mechanism to prevent pollens from fertilizing ovules of the same flower by inhibiting their germination on stigma or pistil.

(iii) Production of unisexual flowers so that male and female parts will be present on different plants (dioecious) or on different flowers in the same plant (monoecious). It prevents both autogamy and geitonogamy.

Ans. In wind-pollinated flowers:

(i) (a) Anthers are well exposed for easy dispersal of pollen grains.

(b) Pollen grains are light and non-sticky so that they can be transported by wind currents.

(c) Stigma is large and feathery to trap pollens.

(iii) Flower rewards their insect pollinators easily by offering: –

(a) Nectar and edible pollen grains.

(b) Safe place for insects to lay eggs by some flowers, e.g. Amorphophallus and Yucca.

Ans. (i) Strategies to prevent self-pollination are:

(a) Pollen grain release and stigma receptivity are not synchronized, either the anther matures first or the stigma.

(b) Anther and stigma are placed at different positions so that the pollens cannot come in contact with the stigma of the same flower.

(c) A genetic mechanism called self-incompatibility, which prevents self-pollen from fertilizing the ovules either by inhibiting pollen germination or by retarding the growth of pollen tube in the pistil.

(d) By producing unisexual flowers. Plants are dioecious and continued self-pollination may cause inbreeding depression.

(ii) Geitonogamy is referred to as genetically autogamy because the pollen grains come from the same plant, though from a different flower.

Ans. (i) Transfer of pollen grains from the anther to the stigma of another flower of the same plant is called geitonogamy. It is functionally cross-pollination as it involves a pollinating agent but is genetically similar to autogamy since the pollen grains come from the same plant (genetically same parent).

(ii) Continued self-pollination results in inbreeding depression because the majority of flowering plants produce hermaphrodite flowers and pollen grains generally come in contact with the stigma of same flower

To discourage this, flowering plants developed many devices. Some of the Strategies to prevent self-pollination are:

(a) Pollen grain release and stigma receptivity are not synchronized, either the anther matures first or the stigma.

(b) Anther and stigma are placed at different positions so that the pollens cannot come in contact with the stigma of the same flower.

(c) A genetic mechanism called self-incompatibility, which prevents self-pollen from fertilizing the ovules either by inhibiting pollen germination or by retarding the growth of the pollen tube in the pistil.

(d) By producing unisexual flowers. Plants are dioecious and continued self-pollination may cause inbreeding depression.

Ans. Significance of seed formation:

• Seed formation is linked with pollination and fertilization that are independent of water and therefore is a more dependable process.
• Seed formation provides protection and nutrition to the developing embryo.
• Seeds are means of multiplication of higher plants. Being capable of perennation, it can withstand variable climate.

Ans. The typical female gametophyte or embryo sac is 8-nucleate and 7-celled. 2 polar nuclei are situated below the egg apparatus in the large centraftfell. Three cells are grouped together at the micropylar end and constitute the egg apparatus. The egg apparatus consists of two synergids and one egg cell.

The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid. Three cells are at the chalazal end and are called the antipodals.

Ans. In this, flowers are not open pollen falls to the stigma of the same flower, and seed setting takes place without the influence of external agency. In geitonogamy transfer of pollen grains from the anther to the stigma of another flower of the same plant. Functionally geitonogamy is a type of cross-pollination but it is genetically similar to autogamy since the pollen grains come from the same plant.

Ans. Examples are as follows:

• Wind-pollinated flowers - Maize, pine
• Water-pollinated flowers - Hydrilla, Vallisneria
• Insect-pollinated flowers - Sweet pea, Salvia

Ans. Difference between Self-pollination and Cross-pollination is as follows: