Figure 38.4 Development of angiosperm gametophytes
Angiosperms
•  Life cycle, fruits, seeds
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Angiosperm seeds consist of diploid and
triploid tissues
Embryo:
Diploid
(from fertilized egg)
Food Supply:
Triploid
Endosperm
(from polar nuclei
and second sperm)
Seed Coat:
Diploid
(from ovule wall)
Why double fertilization?
•  According to one hypothesis, double
fertilization synchronizes development of
food supply (endosperm) with
development of the embryo: if no
fertilization of the egg occurs, no
resources are wasted on building the food
supply
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Remember: Fruit = mature ovary. Pictured below is one kind of dry fruit—a
legume.
Layers of the pericarp
•  Exocarp: outermost “skin”
•  Mesocarp: in the middle
•  Endocarp: innermost layer, closest to the
seed
Note: As the pericarp develops, it often differentiates into
distinct layers, the exocarp, mesocarp, and endocarp (oft.
most conspicuous in fleshy fruits)
Figure 38.9 Classification of Fleshy Fruits
2 main kinds of fruit: dry vs. fleshy
One carpel / one flower
Figure 38.9 Classification of Fleshy Fruits
Many carpels / one flower
Many flowers
Berry: All parts of pericarp are fleshy/pulpy except for exocarp (skin)
This grape is a berry.
A pepo (pumpkin) is a berry with a thick, inseparable rind.
There are 3 main kinds of simple fruits…
A hesperidium (citrus, orange) is a berry with a leathery,
separable rind.
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Drupe (stone fruit): Usually one-seeded with a stony endocarp, fleshy
mesocarp, and a thin and skin-like exocarp .
Pome: develops from flower with inferior ovary and compound pistil.
Receptacle / floral tube becomes major fleshy part of the fruit.
From receptacle
Outer limit of pericarp
Dry fruits: dehiscent vs. indehiscent.
Dehiscent fruits split open at maturity
Fruit and Seed dispersal
Indehiscent fruits do not split open at maturity
Fruit adaptations that enhance seed dispersal: Red berries are animal
dispersed, while dandelion fruits are wind-dispersed (right).
•  Fruits protect seeds during development and
sometimes aid in their dispersal
•  Fleshy fruits or seeds are adapted to animal
dispersal
•  Dry fruits can be adapted to air or water dispersal,
animal dispersal, or to release the seeds at maturity
•  Seeds themselves often have their own dispersaladapted morphology, and adaptations for survival
and germination
Figure 30.x2 A bird eating berries containing seeds that will be dispersed later
with the animal's feces.
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Some fruits, such as these burrs, hitch a ride
on the fur of animals
Don’t forget: many plants also reproduce asexually. Two examples: the
maternity plant (Kalanchoe, left), aspen (Populus) groves (right)
The seeds of many plants have elaiosomes—
fleshy attachments which attract ants. Ants carry
the seeds back to their nests, eat the elaiosome,
and often discard the seed. (One example is our
native wild ginger, Asarum caudatum)
Seed adaptations for survival and
germination
•  Many seeds exhibit dormancy, a temporary condition of
low metabolism and no growth or development. Some
seeds can survive like this for decades or more. What are
the potential benefits of dormancy?
•  Dormancy in some seeds is simply broken by favorable
environmental conditions, but others only germinate after
specific cues
•  What would you expect the cues to be for seeds living in
deserts, fire-prone habitats (such as California chaparral),
or at high latitudes? How about for seeds borne in berries
eaten by mammals?
Figure 38. 8 Review: Three types of seed structure
Figure 38. 8 Review: Three types of seed structure
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Figure 38. 8 Review: Three types of seed structure
The four steps of seed germination: 1. imbibition of water,
2. enzyme digestion of stored food, 3. embryo begins growth and radicle is
pushed through the seed coat, and 4. shoot tip grows toward soil surface.
Germination of a barley seed is shown below.
Figure 38.10 Two ways that young shoots break through the soil surface.
Figure 38.7 The development of a dicot plant embryo
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