Seeds of some plants germinate immdiately after shedding from the plants while in other plants they require a period of rest before germination. The later phenomena is called as dormancy. Give the reasons for seed sormancy and some methods to break it.

Explanation

Reasons for seed dormancy:
(i) Impermeable seed coat to water e.g. Chanopodium.
(ii) Impermeable seed coat to chemicals e.g Xanthium.
(iii) Hard seed coat e.g. Capsella.
(iv) Presence of inhibitors like ABA, phenolics etc.
(v) Due to presence of excess of salts e.g. Atriplex.
(vi) Immature embryos.
Methods for breaking dormancy:
(i) In alimentary canal some seeds get treated with digestive enzymes.
(ii) To give time for ripening of embryo.
(iii) Development of growth hormones like auxins, cytokinins, gibberellins etc.
(iv) By treating them with heat, light, oxidation etc.
(v) By mechanical scarification.
(vi) By chemical scarification.
(vii) By giving chilling treatment.