Chapter 8

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

Dicots MonocotsTwo 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 ringVascular bundles of stem scattered

Pollen grains with three apertures

Pollen grains with one aperture

Two major classes of flowering plants:• Magnoliopsida (dicots) and Liliopsida (monocots)

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

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.

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

– Three 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 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

– Pome - Flesh comes from enlarged floral tube or receptacle that grows up around ovary.o Endocarp papery or

leatheryo 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 baseo 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 as wings for dispersal.– Maples, ashes, elms

• Schizocarp - Twin fruit that breaks into one-seeded segments called mericarps

Corn section

SamarasSchizocarp 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.

Multiple Fruits• Derived from several to

many individual flowers in single inflorescence – Mulberries, Osage orange,

pineapples, figs

o Raspberries, blackberries, strawberries

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

– 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 do not emerge

above surface.

Epigeous germination

Epigeous germination

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