Plant Biology -- Ripening Seeds
Almost all seeds undergo some period of dormancy — if they did not, they would start to grow in the fruits on the mother plant and defeat their principal purposes: dispersal and survival of the germplasm. The period between the formation of the seed and the time when it will germinate is called the after-ripening period, which may be a few days or months depending on the plant.
Seeds of plants native to regions with cold winters almost all require an after-ripening period of cold temperatures before they will germinate. This requirement can be met in horticultural and crop varieties by refrigerating the moist seed for a period of time. This procedure is called stratification. Dormancy of seeds with hard seed coats often can be broken artificially by scarifying the seed — mechanically thinning the seed coat with a file or nicking it with a knife, allowing water and oxygen to penetrate to the embryo.