I. Generalized
seed structure
A. Where the seed comes from
1. Double fertilization
A. Fusion of egg and sperm (zygote)
B. Fusion of two polar nuclei with
second sperm (endosperm)
B. Parts of the seed
1. Embryo (from zygote)
2. Endosperm (may or may not be
present in mature seed)
3. Seed coat (from integuments)
II. Kinds of seeds
A. Dicots - endosperm is partially or
completely absorbed by the embryo by cotyledons
1. Seed coat (external structure)
A. Hilum - place where seed was
attached to plant
B. Micropyle - small opening in the
integuments
2. Embryo
A. Embryo axis
1. Plumule (shoot apex, first foliage
leaves, and epicotyl)
2. Epicotyl (portion beneath leaves)
3. Hypocotyl (portion beneath
cotyledonary node) - think of it as the root/shoot junction
B. Cotyledons
C. Radicle (primary root)
3. Stored food and mineral reserves
(in cotyledons and other tissues)
4. Enzymes and hormones (found
everywhere)
B. Monocots - endosperm is a discrete,
major structural seed unit
1. Seed coat (external structure)
A. Pericarp - fruit wall developed from
the ovary wall
B. Aleurone layer - protein-rich layer
which encases the endosperm
2. Embryo
A. Embryo axis
1. Plumule (shoot apex, first foliage
leaves, and epicotyl)
2. Coleoptile - protective sheath
around shoot apex
3. Epicotyl and hypocotyl (similar to
dicots)
B. Scutellum - one cotyledon
C. Radicle (primary root)
1. Coleorhiza - protective sheath
around root apex
3. Stored food and mineral reserves
(in starchy endosperm, cotyledons, and other tissues)
4. Enzymes and hormones (found
everywhere)
III. Germination
A. Process imbibition and absorption of
water, hydration of tissues, absorption of oxygen, activation of enzymes and
digestion, transport of nutrients to embryo axis, increase in respiration, cell
division & growth, and embryo emergence
B. Hormones - gibberellins (activate
digestion), cytokinins (stimulate cell division), and auxins (cell enlargement)
C. Epigeal emergence (bean) -
elongation of the hypocotyl (cotyledons push above soil surface)
D. Hypogeal emergence (grass) -
elongation of the epicotyl (cotyledons remain below soil surface)
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