Seed development
Ovule formation
Seeds are mature ovules.
Ovules
(seeds)
In angiosperms, the ovules are
produced inside the ovary that
becomes the fruit.
Fruit wall
One or more ovules (seeds) can
be produced per ovary (fruit).
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Seed development
Ovule formation
In gymnosperms, the ovule also develops into the seed, but it is termed a naked
seed because it does not form inside an ovary – no true fruit production.
Ovules (seeds)
Ovules (seeds)
Ginkgo
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Seed development
Ovule formation
The ovule develops in
the base of the flower
called the ovary.
Stigma
Style
The ovary will form the
fruit tissue.
This flower section
shows an ovule at the
stage where the egg
sac has recently been
formed.
Ovary
Integuments
Egg sac
Ovule
The ovule will become
the seed.
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Seed development
Ovule formation
In the angiosperm flower, the female gametophyte consists of nucellar tissue
that is surrounded by either a single or a double outer tissue layer called the
integuments. The integuments will become the seed coat.
Integuments
Integuments
Nucellus
Nucellus
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Seed development
Ovule formation
In the nucellus, a megaspore mother cell forms that will undergo meiosis and
become the female egg cells within the egg sac.
Outer
Integument
Inner
Integuments
Megaspore
mother cell
Nucellus
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Seed development
Ovule formation
Soon after the
completion of meiosis,
the egg sac is formed
and haploid (1n) nuclei
organized according to
their future function.
Ovary
Funiculus
Ovule
A gap is retained
between the enveloping
integuments called the
micropyle.
This is the opening where
the pollen tube will enter
Micropyle
the embryo sac.
Integuments
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Nucellus
Egg sac
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Seed development
Ovule formation
In angiosperms, the most common
arrangement of cells in the embryo sac is
called the Polygonum type and occurs in
about two-thirds of flowering plants.
This type of embryo sac has seven cells
(eight nuclei) that occupy specific
locations that dictate their function.
Egg sac
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Seed development
Ovule formation
Egg sac organization in lily.
Andipodals
Central cell
polar nuclei
Egg and
synergids
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Seed development
Ovule formation
Ovule development over time. A common form of ovule development has the
ovule turn along the placenta (funiculus) and become inverted.
Funiculus
Nucellus
Integuments
Micropyle
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Seed development
Ovule formation
Ovules vary in their orientation and shape in the ovary. Three common types
include orthotropous, anatropous, and hemianatropous.
Ovary
Integuments
Ovule
Egg sac
orthotropous
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anatropous
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hemianatropous
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Seed development
Ovule formation
In most gymnosperms, the female gametophyte is produced in
the axils of the ovulate cone between protective scales.
The ovulate cone
consists of many spirally
arranged ovuliferous
scales subtended by a
cone bract.
Ovulate cone
Each ovuliferous scale
has a pair of ovules on
its surface.
The ovuliferous scale will
form the seed wing that
covers the mature seed.
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Ovuliferous
scale
Spruce
(Picea)
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Seed development
Ovule formation
In gymnosperms, the megaspore mother cell forms in the nucellar tissue
analogous to angiosperm development.
Nucellus
Nucellus
Megaspore
mother
cell
Ovuliferous
scale
Megaspore mother cell
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Seed development
Ovule formation
Within the female gametophyte, two archegonia are formed each
with one haploid egg cell. Only one egg cell will be fertilized and
develop into an embryo within the ovule.
Ovule
Archegonia
Archegonia
Micropyle
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Seed development
Ovule formation
The winged seed contains the embryo that will germinate to start
the next generation.
Spruce (Picea) seed
Seed coat
Embryo
Wing
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Endosperm (1n)
Female gametophyte
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