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Biology
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2. 24-2 Seed Development and Germination
Photo Credit: ©Carl R. Sams II/Peter Arnold, Inc.
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3. Seed and Fruit Development
How do fruits form?
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4. Seed and Fruit Development
As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds.
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5. Seed and Fruit Development
A fruit is a ripened ovary that contains angiosperm seeds.
As seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds.
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Seed Dispersal
How are seeds dispersed?
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Seed Dispersal
Seed Dispersal
Seeds are dispersed by animals, wind, and water.
Seeds dispersed by animals are typically contained in fleshy, nutritious fruits.
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Seed Dispersal
Seeds of many plants are eaten by animals.
These seeds are covered with tough coatings that protect them from digestive chemicals, allowing them to pass through an animal’s digestive system unharmed.
The seeds then sprout in the feces eliminated from the animal.
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Seed Dispersal
Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in the air or to float on the surface of the water.
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Seed Dispersal
Some seeds are encased in winglike structures that spin and twirl, helping them glide from their parent plants.
A coconut is buoyant enough to float in seawater within its protective coating for many weeks.
Tumbleweed plants break off at their roots and scatter their seeds as they are blown by the wind.
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Seed Dormancy
Seed Dormancy
Many seeds will not grow when they first mature.
These seeds enter a period of dormancy, during which the embryo is alive but not growing.
The length of dormancy varies in different plant species.
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Seed Dormancy
What factors influence the dormancy and germination of seeds?
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Seed Dormancy
Environmental factors such as temperature and moisture can cause a seed to end dormancy and germinate.
Seed dormancy can be adaptive in several ways:
allows for long-distance dispersal
allows seeds to germinate under ideal growth conditions
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Seed Germination
Seed Germination
Seed germination is the early growth stage of the plant embryo.
When seeds germinate, they absorb water which causes food-storing tissues to swell and crack open the seed coat.
The young root grows through the cracked seed coat.
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Seed Germination
In most monocots, the single cotyledon remains underground.
The growing shoot emerges while protected by a sheath.
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Seed Germination
Foliage leaves
Young shoot
The corn seedling is a monocot in which the shoot grows directly upward, protected by its sheath.
Germinating seed
Primary root
Corn (monocot)
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Seed Germination
In dicots, germination takes place in one of two ways.
In some species, the cotyledons emerge above ground, protecting the stem and first foliage leaves.
In other species, the cotyledons stay underground and provide a food source for the growing seedling.
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Seed Germination
Foliage leaves
Young shoot
Cotyledons
Cotyledons
Seed coat
The garden bean is a dicot in which the cotyledons emerge aboveground.
Primary root
Germinating seed
Bean (dicot)
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24-2
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24-2
A germinating corn seedling has
a single cotyledon, which remains below ground.
two cotyledons, which push above ground.
a single cotyledon, which pushes above ground.
two cotyledons, which remain below ground.    
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24-2
Angiosperm fruits develop from
the ovary wall of the flower.
seed endosperm.
swollen sepals of the flower.
flower stamens.
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24-2
An example of a seed that is transported by water is a
coconut.
tumbleweed.
blackberry.
maple seed.
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24-2
The seeds of many plants that form fruits are dispersed mainly by
animals.
water.
wind.
the plant itself.
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24-2
An environmental condition that can cause the activation of a dormant seed is
a sharp drop in temperature.
the heat from a forest fire.
an extended drought.
falling from a great height.
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25. END OF SECTION