Flowers, Fruits, and Seeds

Chapter 8

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 2 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

2 major classes of flowering plants:• Magnoliopsida (dicots)

• Liliopsida (monocots)

Dicots Monocots

2 cotyledons 1 cotyledonFlower parts in multiples of 4 or f5

Flower parts in multiples of 3

Leaves with distinct network of veins Leaves with parallel 1° 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 3 apertures

Pollen grains with 1 aperture

Structure of Flowers Flowers begin as embryonic primordium that

develops into bud Flowers occur as specialized branches at tips of

peduncles• May have branchlets of pedicels

Receptacle - swollen end of peduncle or pedicel• Other parts of flower attached to receptacle in

whorls: sepals, petals, stamens, and pistil

Structure of Flowers

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 1 to several carpels

Structure of Flowers 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

– Develop from flower ovaries and found exclusively in flowering plants

Tomato fruit

Fruits Fruit Regions• Exocarp – skin

• Endocarp - inner boundary around seed(s)

• Mesocarp - tissue between exocarp and endocarp

• 3 regions collectively called pericarp

Peach fruit

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 1 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 >

1 seed, and with fleshy pericarp

−True Berry - with thin skin and relatively soft pericarp Tomatoes, grapes, peppers,

blueberries, bananas−Pepo - relatively thick rind

Pumpkins, cucumbersGrape berries

Fruits

• Pome – flesh from enlarged floral tube or receptacle that grows up around ovary– Endocarp papery or

leatheryApple pomes

• Berry cont’d.− Hesperidium - leathery skin containing oils

Citrus

Apples, pears - core and little of adjacent tissue from ovary; remainder from floral tube and receptacle

Fruits Dry Fruits - mesocarp dry at maturity• Dehisicent or indehiscent

Dehiscent fruits - split at maturity • Follicle - splits

along 1 side

– Larkspur, milkweed, peony

• Legume - splits along 2 sides

– Legume family: peas, beans, lentils, peanuts

Milkweed follicle

Legumes

Fruits Dehiscent fruits cont’d.• Siliques and Silicles - split along 2 sides, but seeds on

central partition, which is exposed when 2 halves separate

– Silique - more than 3 times longer than wide

– Silicle - less than 3 times longer than wide

– Mustard family: broccoli, cabbage

Silicle

Silique

Fruits Dehiscent fruits cont’d.• Capsules - consist of at least 2 carpels, and split in

variety of ways−Irises, poppies, violets, snapdragons

Capsules

Fruits Indehiscent Fruits – don’t split at maturity• Single seed united

with pericarp

– Achene - base of seed attached to pericarp Sunflower seed,

buttercup, buckwheat

Inside of sunflower

achene

Fruits Indehiscent Fruits cont’d.

– Nut - similar to achene, but larger, with harder and thicker pericarp, and cluster of bracts at base Acorns,

hazelnuts, hickory nuts Acorn

Fruits Indehiscent Fruits cont’d.– Grain (Caryopsis) - pericarp tightly

united with seed Grasses: corn, wheat, rice, oats

−Samara - pericarp extends as wings for dispersal. Maples, ashes, elms

−Schizocarp - twin fruit that breaks into one-seeded segments called mericarps

Corn section

Samaras 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.

Raspberries, blackberries, strawberries

Multiple Fruits• Derived from several to many

individual flowers in single inflorescence

Mulberries, Osage orange, pineapples, figs

Blackberry aggregate fruits

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

Bean seed

Seeds Structure cont’d.

– Epicotyl - stem above cotyledon attachment

– Hypocotyl - stem below cotyledon attachment

– Radicle - tip of embryo that develops into root

Bean seed

Seeds

• Hypocotyl lengthens, bends and becomes hook-shaped

• Top of hook emerges from ground, pulling cotyledons above ground

Hypogeous germination• Hypocotyl remains short and cotyledons don’t emerge

above surface

Epigeous germination

Epigeous germination

Germination Germination - 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 Scarification - artificially breaking dormancy

• After ripening - embryo composed of only a few cells when fruit ripens; seeds won’t germinate until embryo develops

Germination Favorable environmental factors needed for

germination• H2O and O2

• Light or its absence• Proper temperature range

Enzymes in cytoplasm begin to function after H2O 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 still on parent Vivipary in red mangrove

Review Introduction Differences Between Dicots and Monocots Structure of Flowers Fruits Fruit and Seed Dispersal Seeds