A seed is, in essence, an embryonic dormant plant awaiting appropriate conditions to grow. Seed dormancy allows for seedling survival, increased dispersal of the seed, and synchronized germination of seeds.
Seed dormancy can occur in several forms. Ecodormancy is a controlling factor. In simple seed dormancy, if a seed does not have sufficient water for imbibition, optimum temperature conditions, or an appropriate light and gaseous environment, it will not germinate and grow, although alive and carrying on metabolic activity at a low rate.
Some seeds have evolved physical, paradormancy mechanisms. For instance, certain seeds have hard, sclerified seed coats (testa) or other outer coverings that are not easily penetrated by water or gases. Dormancy control is not removed until the seed coat or surrounding tissue has been broken, scarred, exposed to digestive acids of animals that aid in their dispersal, decomposed either chemically by soil acids or biologically by soil microorganisms, or physically removed. For horticultural purposes, some seeds require scarification—physical scarring by abrasives or organic acids, or cracking and removal. For example, a peach "pit" is actually a sclerified, bony endocarp tissue containing a seed. This protective pit prevents rapid water entry and must be removed, cracked, or chemically dissolved in order for the seed inside to germinate and grow.
Seeds of most temperate zone fruit also express endodormancy; they must be exposed to a period of cool, moist conditions prior to germination. The cool, moist requirement is called "stratification." Stratification may be a relatively short period (days to weeks) or repeated cycles of cooling followed by warm weather (repeated years) to ensure that seeds last over several winter seasons. For nursery operators and propagators, knowledge of the stratification requirements of specific seeds is essential if a high degree of germination is to be achieved. Seeds can have multiple dormancy mechanisms to ensure their survival and dispersal. It is common that ecodormancy of seeds overlaps their endodormancy, so that even though the endodormancy requirements are met after the appropriate stratification period, they will not germinate and grow until the appropriate environment for that growth is apparent to the seed.
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