Germination ~ Types , Necessary Conditions


The process in which the embryo emerges out of the seed by rupturing the seed coat, leading to the formation of a seedling is called germination.

Conditions necessary for Germination:

Water: When water enters the seed, it activates the enzymes present in the seed. These enzymes mobilise the reserve food and break it into simpler forms. This food is utilised by the embryo, and the embryo begins to grow.

Temperature: A moderate temperature, ranging from 25°C to 35°C is favourable for the seeds to germinate. Such a temperature is known as optimum temperature.

Oxygen: Oxygen provides energy through respiration for rapid cell division and cell growth.

Light: Seeds of plants do not germinate unless they are exposed to a certain duration of light.

Also Read Pollination and Fertilization

Types of Germination

Hypogeal :

The epicotyl elongates and the cotyledons remain underground. Examples: Pea, gram, maize, wheat etc.

Epigeal :

The hypocotyl elongates and the cotyledons are pushed above the ground. Examples: Bean, castor, sunflower, gourd etc.

Also Read Fertilization ~ In Humans & Plants

Viviparous :

The seed germinates while it is still inside the fruit, attached to the mother plant. Examples: Rhizophora, Sonneratia

Difference Between Epigeal And Hypogeal Germination

It is a type of germination whereby the seed leaves or the cotyledons are brought on to the surface or above the soil along with the shoot during germination.  It is a type of germination whereby the seed leaves or the cotyledons remain below the soil surface during germination.
The cotyledons are brought out of the soil by the excessive growth of the hypocotyl.  The hypocotyl does not elongate much. Instead, the epicotyl grows and takes the plumule above the soil. 
The plumule comes out of the seed coat by the elongation of the hypocotyl.  The plumule comes out of the seed coat by the elongation of epicotyl.  
The energy for growth is primarily derived from cotyledon.The energy for growth is primarily derived from the endosperm.
Generally dicot seeds show this type of germination (Epigeal). Generally monocot seeds show hypogeal germination. 

The seedling is a stage in plant growth where the plant is still dependent on the reserve food of the seed or the food manufactured by the cotyledons.
The seedling consists of five parts—the radicle or embryonic root, hypocotyl, epicotyl, plumule and cotyledons.

You may read Tissues: Plant and Animal Tissues

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