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Morphology of Flowering Plants

The Root (Group B)

Germination is the process during which seed reserves present in the seed are broken down and the embryo starts to grow.

During germination, the seed absorbs water. Germination is irreversible i.e. once begun; the seed cannot be brought back to dormant state,

Seeds which do not germinate even after provided with all the conditions necessary for germination are called dormant seeds and the phenomenon is termed as dormancy.

Let us study what happens during germination

When a seed is germinating, the portion above the cotyledon that forms future shoots is called plumule and the portion below the cotyledon that forms the future roots is called radicle.

Conditions Necessary for Germination

Activity 1

  • As shown in the figure, take a beaker with water and place it in, a glass slide with three bean seeds tied to it.

  • The slide should be kept in such a way that the upper seed is completely out of water, lower seed is completely submerged in water and the middle seed is half submerged in water.

  • The beaker is placed in warm temperature (25° C − 30° C) for few days.

Result

  • Seed at top − Does not germinate

  • Seed at middle − Germinates

  • Seed at bottom − Does not germinates

Inference

  • Seed at top gets only oxygen and no water. So it does not germinate.

  • Seed at middle receives both oxygen and water. So it germinates.

  • Seed at bottom gets only water and no oxygen. So it does not germinate.

Activity 2

  • Take two petridishes with moist cotton placed in it.

  • Place a few soaked seeds in both petridishes.

  • Place the first petridish in refrigerator (4°C) and the second one at room temperature (30°C).

  • Leave the petridishes for few days.

Result

  • No germination was seen in the petridish kept in refrigerator while the seed present in the petridish kept at room temperature germinates.

Inference

  • Suitable temperature is necessary for germination.

 

Structure of Monocot Seed

  • In seeds of cereals, seed coat is membranous and fused to the fruit wall.

  • Generally, monocot seeds are endospermous. Endosperm is bulky and stores food.

  • Aleurone layer - proteinous layer that separates embryo from outer covering of endosperm

  • Embryo is situated in a groove in endosperm. Embryo consists of

    • cotyledon known as scutellum

    • embryonal axis (consisting of plumule and radical)

  • Plumule is enclosed in a sheath called coleoptile and radical in coleorrhiza.


So what does you concluded about the necessary conditions for seed germination?

Seeds require water, suitable temperature, and oxygen for germination. Let us see how these factors affect germination one by one.

Water

  • Helps in rupture of seed coat by swelling the seed, so as to allow the elongated radicle to come out during germination
  • Necessary for various biochemical reactions occurring within the seed
Suitable Temperature 
  • Moderately warm temperature (25ºC - 35°C) is suitable for germination of most of the seeds.
  • Very low or high temperature can destroy the delicate tissues of the seed.
Oxygen
  • Necessary for providing energy (through respiration) required for rapid cell division and cell growth



Types of Germination

There are two types of germination patterns depending upon the behaviour of cotyledons during germination.

  • Epigeal germination

  • Hypogeal germination

Epigeal Germination

When the cotyledons are lifted above the ground as a result of rapid elongation of hypocotyls e.g. seeds of bean, castor, cotton, etc germinate …

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