Chapter 6
Lecture Outline
Flowers, Fruits, and
Seeds
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Outline

Introduction

Differences Between Dicots and Monocots

Structure of Flowers

Fruits

Fruit and Seed Dispersal

Seeds
Introduction

Annual plants - Cycle completed in single
season.
• Cycle = from seed germination to mature plant
producing seeds

Biennial plants - Cycle completed in two
growing seasons.

Perennial plants - Cycle takes several to many
growing seasons or plant produces flowers
on new growth, while other plant parts persist
indefinitely.
Differences Between Dicots and Monocots

Two major classes of flowering plants:
•
Magnoliopsida (dicots) and Liliopsida (monocots)
Dicots
Monocots
Two cotyledons
One cotyledon
Flower parts in multiples of four
or five
Flower parts in multiples of three
Leaves with distinct network of
veins
Leaves with parallel primary veins
Vascular cambium and cork
cambium present
Vascular cambium and cork
cambium absent
Vascular bundles of stem in ring
Vascular bundles of stem scattered
Pollen grains with three
apertures
Pollen grains with one aperture
Structure of Flowers

Flowers begin as embryonic primordium that
develops into a bud.

Flowers occur as specialized branches at
tips of peduncles.
• May have branchlets of pedicels (stalk of single
flower)

Receptacle - Swollen end of peduncle or
pedicel
• Other parts of flower attached to receptacle in
whorls: sepals, petals, stamens, and pistil.
Structure of Flowers

Sepals - Outermost whorl
• Collectively referred to as calyx
• Protects flower while in bud

Petals - Next whorl inside sepals
• Collectively referred to as corolla
– Showy corollas attract pollinators.
– Inconspicuous or missing corollas in many trees, weeds,
grasses, and wind-pollinated plants
• Calyx and
corolla form
perianth in
monocots
Structure of Flowers

Stamens attached around base of pistil.
• Each stamen consists of filament with anther at top.
–

Pollen grains developed in anthers.
Pistil consists of stigma, style, and ovary.
• Ovary develops into fruit.
Structure of Flowers

Ovaries evolved from carpels with margins
rolled inward.
• Carpel - Leaf with ovules on margins
– Carpels may be fused together into compound ovary.
– Pistil can consist of one to several carpels.

Superior Ovary - Calyx and corolla attached to
receptacle at base of ovary.

Inferior Ovary - Receptacle grows up and
around the ovary.
• Calyx and corolla appear attached at top of ovary.

Ovary contains ovules.
• Ovules develop into seeds after fertilization.
Structure of Flowers

Flowers can be produced singly or in
inflorescences.
• Inflorescence - Group of flowers
Fruits

Fruit - Matured ovary and its accessory parts
• Contains seeds
• All fruits develop from flower ovaries and
accordingly are found exclusively in flowering
plants.
Tomato
fruit
Fruits

Fruit Regions
• Exocarp - Skin
• Endocarp -
Inner boundary
around seed(s)
• Mesocarp Tissue between
exocarp and
endocarp
–
Peach fruit
Three regions collectively called pericarp.
Fruits

Variability of fruits
• Can consist of only ovary and seeds
• Can include adjacent flower parts
• May be fleshy or dry at maturity
• May split or not split
• May be derived from a one or more ovaries
Fruits

Fleshy Fruits - Mesocarp at least partly
fleshy at maturity.

Simple fleshy fruits develop from flower with
single pistil.
• Drupe - Simple
fleshy fruit with
single seed
enclosed by hard,
stony endocarp (pit)
Drupes: peaches,
almonds, olives
Fruits

Simple fleshy fruits
• Berry
–
From compound ovary, with
more than one seed, and with
fleshy pericarp
–
True berry - With thin skin and
relatively soft pericarp
o
–
Tomatoes, grapes,
peppers, blueberries,
bananas
Pepo - Relatively thick rind
o
Pumpkins, cucumbers
Grape berries
Fruits
• Berry
– Hesperidium - Leathery skin containing oils
o Citrus
–
Pome - Flesh comes from
enlarged floral tube or
receptacle that grows up
around ovary.
o
Endocarp papery or
leathery
o
Apples, pears - Core
and a little of adjacent
tissue is from ovary;
remainder is from floral
tube and receptacle
Apple pomes
Fruits

Dry Fruits - Mesocarp dry at maturity
• Dehisicent or indehiscent

Dehiscent fruits - Split at Maturity
• Follicle - Splits
along one side
–
Larkspur,
milkweed, peony
• Legume - Splits
along two sides
–
Legume family:
peas, beans,
lentils, peanuts
Milkweed follicle
Legumes
Fruits

Dehiscent fruits
• Siliques and silicles - Split along two sides, but
seeds on central partition, which is exposed when
two halves separate.
–
Silique - More than
three times longer
than wide
–
Silicle - Less than
three times longer
than wide
–
Mustard family:
broccoli, cabbage
Silicle
Silique
Fruits

Dehiscent fruits
• Capsules - Consist of at least two carpels, and
split in a variety of ways
–
Irises, poppies, violets, snapdragons
Capsules
Fruits

Dry Fruits

Indehiscent Fruits - Do Not Split at Maturity
• Single seed united with
pericarp
–
–
Achene - Base of seed
attached to pericarp.
o Sunflower seed,
buttercup, buckwheat
Nut - Similar to achene,
but larger, with harder
and thicker pericarp, and
a cluster of bracts at base
o Acorns, hazelnuts,
hickory nuts
Inside of
sunflower
achene
Acorn
Fruits

Indehiscent Fruits
• Grain (Caryopsis) - Pericarp tightly
united with seed
–
Grasses: corn, wheat, rice, oats, barley
• Samara - Pericarp extends
Corn section
as wings for dispersal.
–
Maples, ashes, elms
• Schizocarp - Twin
Samaras
fruit that breaks
into one-seeded
segments called
mericarps
–
Schizocarp of mericarps
Parsley family: carrots, anise, dill
Fruits

Aggregate Fruits
• Derived from single
flower with several to
many pistils
–

Individual pistils mature
as clustered unit on
single receptacle.
o Raspberries, blackberries,
strawberries
Blackberry aggregate fruits
Multiple Fruits
• Derived from several to
many individual flowers
in single inflorescence
–
Mulberries, Osage orange,
pineapples, figs
Osage orange multiple fruit
Fruit and Seed Dispersal

Dispersal by Wind
• Fruits: Samaras,
plumes or hairs on
fruit
• Seeds: Small and
lightweight, or with
wings
Fruit and Seed Dispersal

Dispersal by Animals
• Seeds pass through
digestive tract.
• Fruits and seeds adhere
to fur or feathers.
• Oils attract ants.
–

Elaiosomes on bleeding
hearts used as food by
ants.
Seeds from bleeding hearts.
Elaiosome is white.
Water Dispersal
• Some fruits contain trapped air for floatation.
Seeds

Structure
• Ovules develop into seeds.
–
Cotyledons - Food storage organs that function as
“seed leaves”
–
Embryo = cotyledons and plantlet
–
Plumule - Embryo shoot
–
Epicotyl - Stem above
cotyledon attachment
–
Hypocotyl - Stem below
cotyledon attachment
–
Radicle - Tip of embryo
that develops into root
Bean seed
Seeds

Epigeous germination
• Hypocotyl
lengthens, bends
and becomes
hook-shaped.
• Top of hook
emerges from
ground, pulling
cotyledons
above ground.
Epigeous germination

Hypogeous germination
• Hypocotyl remains short and cotyledons do not emerge
above surface.
Germination

Germination is beginning or resumption of
seed growth.
• Some require period of dormancy.
–
Brought about by mechanical or physiological factors,
including growth-inhibiting substances present in seed
coat or fruit
–
Break dormancy by mechanical abrasion, thawing and
freezing, bacterial action, or soaking rains.
o
Scarification - Artificially breaking dormancy
• After ripening - Embryo composed of only of few
cells when fruit ripens; seeds will not germinate
until embryo develops.
Germination

Favorable environmental factors needed for
germination.
• Water and oxygen
• Light or its absence
• Proper temperature range

Enzymes in cytoplasm begin to function
after water is imbibed.
Longevity

Seed viability varies,
depending on species
and storage conditions.
• Viability extended:

–
At low temperatures
–
When kept dry
Vivipary - No period of
dormancy; embryo
continues to grow while
fruit is still on parent.
Vivipary in red mangrove
Review

Introduction

Differences Between Dicots and Monocots

Structure of Flowers

Fruits

Fruit and Seed Dispersal

Seeds