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The growth of a seed is completely arrested after it is fully developed. Such seeds will germinate if they are supplied with water and suitable temperature. In many cases the seeds do not germinate even if they are provided with all the best conditions. The completely dry ripe seed is physiologically inactive and is said to be in a resting stage. The seed is said to be dormant and the phenomenon is termed as dormancy.


Factors Responsible for Dormancy

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Hard Seed Coat

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The hard seed coat can cause dormancy in plants

i) By being impermeable to water the impermeability of seed coat to water and oxygen does not allow the seed to germinate.

ii) In certain wild plants the hard seed coat acts as a physical barrier to the expansion of the embryo.

Immature Embryo

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In certain plants the seeds are shed before the embryo is mature. So the seed undergoes dormancy to allow the embryo to develop.

Presence of Chemical Inhibitors

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Presence of certain inhibitory substances such as ABA, coumarin, phenolic acids, short chain fatty acids in the embryo causes seed dormancy. The seeds remain dormant as long as the concentration of these inhibitory substances remain high within the seeds.

Period of after Ripening

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Seeds of apple, peach, iris would not germinate even when the conditions for germination are favourable. Such seeds germinate after they have completed a period of rest, which is called period of after ripening.

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