POLLINATION AND GERMINATION

POLLINATION

 The process in which pollen grains from anther of male flower are transferred to stigma of female flower is called pollination. Usually the water, air, wind, insects such as bees acts as agents of pollination.

Pollination can happen in two ways:  natural pollination and artificial pollination. 

Wind, water, insects and animals such as birds and bats pollinates the flowers and thus acts as natural pollinators. These pollinators transfer the pollen grains from the anther of one flower to stigma of another flower . 

TYPES OF NATURAL POLLINATION

 There are two types of natural pollination. 

 Cross pollination: when pollen grains from the anther of one flower is transferred to stigma of another flower of same species, it is called cross pollination. This pollination occurs between flowers of two different  individual plants but of same species. 

Self pollination:  When pollen grains are transferred from an anther to the stigma of same flower , it is called self pollination. This pollination occurs between flowers of the same plant. 

ARTIFICIAL POLLINATION

Sometimes when plants with desirable characters such as large fruits, less seeds, disease resistant plants etc are to be produced, then humans do this by artificial pollination. 

When pollination does not occur naturally but is carried out by artificial means, it is called artificial pollination. 

In this method, The pollens are collected from the flower (whose anthers are removed before producing pollen ) with the help of needle and  forecep. The flower is covered with a polythene bag to collect the pollen. Now this collected pollen is then blown on the stigma of other parent plant with the help a paint brush. This pollinated flower is then covered with another polythene bag to prevent otherpollens to reach the flower. 

The two parent plants chosen should have desirable characters which would then be carried to new plant. One parent may be selected for its healthy growth and the other for its good fruits. The  new plant produced will have both the characters. Such a new plant obtained after artificial pollination is called as hydrid. This process by which an entirely different kind of  a plant or animal is produced thought artificial method is called Hybridization. 

This method helps to improve the quality and quantity of many plants and even disease resistant varieties can be produced by this process. 

GERMINATION 

 A new plant is produced only after the fertilization. 

When a pollen grain falls on stigma, it forms a pollen tube which travels all along the length of style and reaches the ovule. There the male nucleus from pollen tube fuses with egg cell and results in the formation of a zygote. This is called fertilization. 

After fertilization, the zygote changes into embryo which finally changes into seed. The ovary changes into fruit which encloses the seed. 

Parts of a seed 

When the embryo changes into seed, bt he surrounding wall gets hardens and forms the tough seed coat. Inside this seed coat, a pair of flehy cotyledons Or seed leaves are found. The developing embryo or baby plant is found in between these seed coats. The embryo consists of a baby root called  radicle and a baby shoot called plumule is found. The space between the radicle abd plumule that develops into stem is called hypocotyl. 

Based on the number of cotyledons, the plants can be classified as monocotyledonous Or monocots that have one seed leaf and Dicotyledonous Or dicots that have two seed leaves. 

ACTIVITY 1 

TO FIND OUT THE NUMBER OF COTYLEDONS 

 Take few bengal gram seeds and corn seeds and soak them in water for 2 to 3 hours. Drain the water and then try to break the seeds from the middle. You observe that corn seed is crushed while bengal gram seeds can be broken into two similar halves. Hence you can say that bengal gram seeds are dicots and corn seed is a monocot. 

Germination 

When the conditions are favourable, seeds germinate and produce new plants. This process is called germination. 

Most of the seeds undergo a resting period before germination. This period is called dormancy. This period may vary from plants to plants may be from few days to few weeks to whole season. The ability of seeds to germinate after a period of dormancy is called viability. 

Conditions necessary for germination. 

* water : Seeds will be dry and dormant before germination. Hence when they get sufficient water or moisture in the soil, they absorb water and swell up. The cotyledons open up and allow the embryo to grow. 

But when the water is excess in soil, it may lead to the development of fungi, hance damaging the seeds. The seeds do no germinate in excess water. 

*Oxygen : As humans, plants also require oxygen for respiration as it releases energy needed for growth. The seeds can not germinate in the absence of oxygen. 

*Temperature: The most favourable temperature for the seeds to germinate is 15 to 40 degrees. The seeds may not germinate if the temperature is below 10 or above 50 degrees. 

TYPES OF GERMINATION

Hypogeal germination:

When the cotyledons remain underground and do not cone above the ground and function only as food source, it is called hypogeal germination. ( 'hypo' means below and 'geal' means earth) Eg: pea and maize plant. 

Epigeal germination:

When the hypocotyl extends and brings the cotyledons above the ground to form the first new green leaves, it is called epigeal germination. ('Epi' means above and 'geal' means earth). Eg: bean and castor.