<P> Some live seeds are dormant and need more time, and / or need to be subjected to specific environmental conditions before they will germinate . Seed dormancy can originate in different parts of the seed, for example, within the embryo; in other cases the seed coat is involved . Dormancy breaking often involves changes in membranes, initiated by dormancy - breaking signals . This generally occurs only within hydrated seeds . Factors affecting seed dormancy include the presence of certain plant hormones, notably abscisic acid, which inhibits germination, and gibberellin, which ends seed dormancy . In brewing, barley seeds are treated with gibberellin to ensure uniform seed germination for the production of barley malt . </P> <P> In some definitions, the appearance of the radicle marks the end of germination and the beginning of "establishment", a period that utilizes the food reserves stored in the seed . Germination and establishment as an independent organism are critical phases in the life of a plant when they are the most vulnerable to injury, disease, and water stress . The germination index can be used as an indicator of phytotoxicity in soils . The mortality between dispersal of seeds and completion of establishment can be so high that many species have adapted to produce large numbers of seeds . </P> <P> In agriculture and gardening, the germination rate describes how many seeds of a particular plant species, variety or seedlot are likely to germinate over a given period . It is a measure of germination time course and is usually expressed as a percentage, e.g., an 85% germination rate indicates that about 85 out of 100 seeds will probably germinate under proper conditions over the germination period given . The germination rate is useful for calculating the seed requirements for a given area or desired number of plants . In seed physiologists and seed scientists "germination rate" is the reciprocal of time taken for the process of germination to complete starting from time of sowing . On the other hand, the number of seed able to complete germination in a population (i.e. seed lot) is referred as germination capacity . </P> <P> Seed quality deteriorates with age, and this is associated with accumulation of genome damage . During germination, repair processes are activated to deal with accumulated DNA damage . In particular, single - and double - strand breaks in DNA can be repaired . The DNA damage checkpoint kinase ATM has a major role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed . </P>

When does germination take place for angiosperm seeds