Flowers and Fruit

Chapter 9


Flower - Sterile Parts


–sepals collectively known as the calyx


–petals collectively known as the corolla


Flower - Fertile Parts

•Stamens – male reproductive organs



•pollen grains develop here


Flower - Fertile Parts

•Pistil = female reproductive organ



–Ovary, contains ovules

•Ovules mature into seeds

•Ovary matures into fruit

Flower parts

•Not all flowers have all parts

•Four basic parts are:





•Each of these sets of parts may form a whorl or a series of spirals, with sepals outermost, pistils innermost


Flower symmetry

Simple and compound pistil

Ovary position

Ovary position and insertion of parts


Inflorescence parts

Inflorescence = a cluster of flowers on a common stem



Pollination Strategies

•Pollination is transfer of pollen grains from anther to stigma

•Fertilization occurs later after sperm of pollen unites with egg within ovary

•Cross-pollination: pollen from a different individual plant

•Self-pollination: pollen from the same flower

•Many plants have mechanisms to prevent self-pollination

–Reduces genetic variability of next generation

–Some plants are dioecious: separate sexes on different plants (monecious)

–Many flowers release pollen before stigma is receptive

–Many plants are self-incompatible due to genetic makeup – prevents self-pollination

Advertising by Flowers


•May have attractive colors / patterns (esp in UV light)

•May be food sources


–Nectar in nectaries

•May have attractive odors

•May aid pollination by shape of flower

–May force pollinator to rub against stamen

•May have shapes like animals’ mates – form of mimicry

•May release pollen to the wind or water

Advanced flower design evolved to match specific pollinators

•Flowers that attract bees

–Blue and yellow flowers

–Nectar and nectar guides

–Bilateral symmetry with “landing pad”

–Ultraviolet patterns on flowers visible to bees


Ultraviolet Patterns Guide Bees to Nectar

“Pollinating” a Pollinator

•weight of bee on “landing pad” releases spring-loaded stamens and stigma


•Flowers generally white or dull in color

•Strong yeasty, spicy, or fruity odors


•Flowers dull red or brown

•Foul odors

•Flowers called "carrion flowers"



Moths and Butterflies

•Usually white or yellow, sometimes orange or red in color

•Sweet fragrances

•Nectar often produced at base of long corolla tube or spur, need long sucking mouthparts to access


•Flowers bright red or yellow and large inflorescences

•Produce copious quantities of nectar in long floral tubes

•No odor


•Generally tropical flowers that open at night

•Large flowers or ball-like inflorescences

•Easily accessible

•Copious nectar

•Heavy scent

Orchid Adaptations for Pollination

•Pollen grains produced in little sacs called pollinia

•Pollinia either stick to the insect pollinator or are forcibly "slapped" on the insect by a trigger mechanism

•Petals modified to resemble female wasp or bee

– male insects attempt to mate with flower and pick up pollinia in the process

•Other adaptations include underwater trapdoors and powerful narcotic fragrances


Wind pollination

Wind-pollinated flowers:


•No petals or sepals

•Dull colors


•No nectar

•More common in temperate than tropical regions


–When do they flower?


Monocots and Dicots

•Typical features of monocots and dicots

•Review in lab

Life cycle of flowering plants

•Flowers are produced by adult plants

•Egg and other cells present in ovule(s) within ovary of pistil

•Two sperm are ultimately produced within pollen grains

•Pollen grain lands on receptive stigma

•Pollen tube grows through style, enters ovule

•One sperm fertilizes egg, becomes zygote, then embryo

•Other sperm fertilizes pair of other cells, becomes endosperm for seed

•Ovule becomes seed, ovule walls become seed coat

•Ovary becomes fruit

Double Fertilization

Pollination vs. Fertilization

•Which comes first?

Seed and Fruit Dispersal

movement of seed or fruit away from parent plant



•eaten (pass through gut)

•cached (escape being eaten)

•carried (grab onto animal)


Wind dispersed seeds and fruit

Wind dispersed seeds and fruit

Animal dispersed: eaten

Animal dispersed: cached

Animal dispersed: mostly carried


•Seeds have oily appendage which ants feed to their larvae

•Remainder of seed is discarded, and can germinate into healthy plant

•Ants disperse bleeding hearts, inside-out flower, trilliums, wild ginger in PNW forests.

Asexual Reproduction


–Preservation of parental genotype – offspring are genetically identical to parent and are equally “fit” for environmental conditions


–Populations are less able to adapt to changing environmental conditions – parasites, nutrient availability, competition from other species, climate