plants-seeds-1 - When conditions become suitable for...

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Seeds and germination - seed structure A seed is the product of sexual reproduction in flowering plants. In dicotyledonous plants the seed consists of a miniature plant, the embryo and two modified leaves, the cotyledons , swollen with food reserves. Fig.1 Seed structure of a dicotyledon Testa The seed coat; encloses and protects the seed from insects and fungi. It is usually hard and dry. Micropyle Hole which admits water when the seed starts to germinate. Plumule The embryo shoot; two leaves and a growing point. Cotyledons Modified leaves containing food reserves. Radicle Embryo root. Epicotyl The section of stem above the cotyledon stalk. Hypocotyl The section of stem below the cotyledon stalk. Germination is the process by which the embryo grows and develops, eventually becoming a fully mature plant. The pattern of germination is similar in most dicotyledonous seeds. When the seed is shed, it is usually dry and hard, containing very little water. In this dehydrated state it is best suited to withstand drought and extreme temperatures.
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Unformatted text preview: When conditions become suitable for germination, the seed takes in water through its micropyle. The tissues absorb water and swell and the testa becomes soft. The radicle grows first, pushing though the testa and entering the soil. Next, either the hypocotyl or the epicotyl, depending on the species, starts to elongate and carry the plumule upwards through the soil. Elongation of the epicotyl brings the embryo out from between the cotyledons and through the soil, leaving the cotyledons below ground. Elongation of the hypocotyl brings the cotyledons and the plumule above ground. Whichever pattern of germination occurs, the energy and raw materials required for growth come from the food (usually starch) stored in the cotyledon. testa plumule radicle micropyle cotyledon (a) Longitudinal section cotyledons plumule epicotyl cotyledon stalk hypocotyl radicle (b) Diagram of seed structure 1 Seed structure © D.G. Mackean...
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This note was uploaded on 11/29/2011 for the course BIO 218 taught by Professor Young during the Fall '11 term at BYU.

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