GERMINATION IN PLANTS.

GERMINATION IS THE GROWTH OF PLANT INTO SEEDLING.It starts when seeds become active below ground , and ends when the first foliage leaves appears above the ground .A seed consists of an embryo and the food store ,surrounded by a testa (seed coat). The embryo is made up of one or two cotyledons (seed leaves),attached to a central axis .The upper part of the axis consists of an epicotyl,which has a plumule (embryonic shoots), at its tip.The lower part of the axis consists of hypocotyl and a radicle (embryonic root). After dispersal from the parent plant , the seeds dehydrate and enter a period of dormancy .Following this dormant period , germination begins , provided that the seeds have enough water, oxygen,warmth ,and in some cases,light.In the first stages of germination ,the seed takes in some water;the embryo start to use its food store ;and the radicle swells , break through the testa, and grows downwards.Germination then proceeds in one of two ways depending on the type of seed .In epigeal germination ,the hypocotyl lengthens ,pulling the plumule and its protective cotyledons out of the soil .In hypogeal germination the cotyledons remain below ground and the epicotyl lengthens,pushing the plumule upwards.

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