Flowers, Fruits,
& Seeds
In this chapter you will learn about the
structure and parts of flowers and modifications; compare dicots and monocots;
the nature and development of fruits and fruit structure and parthenocarpy.
You will learn to list and describe various types of fleshy and dry fruits as well as the
agents of fruit and seed dispersal. Finally you will examine seed structure and germination and
recognize dormancy
and longevity of seeds, stratification, and vivipary.
At the end of this chapter the successful student will be able to
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Dicots versus Monocots Seeds |
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Dicots | Monocots |
- Two cotyledons
- Flower parts in fours or fives
- Leaves with distinct vein network
- Vascular cambium present
- Vascular bundles in ring
- Pollen grain with three apertures
|
- One cotyledon
- Flower parts in threes
- Leaves with parallel primary veins.
- Vascular cambium absent
- Vascular bundles scattered
- Pollen grain with one aperture
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- Each flower, which begins as an embryonic primordium that develops into a
bud, occurs as a specialized branch at the tip of a peduncle which may have
branchlets of pedicles.
- Pedicle swells at its tip into a small pad (receptacle).
- Other parts of the flower are attached to the receptacle.
- Outermost whorl typically consists of three to five sepals.
- Sepals (calyx) may be fused together.
- Next whorl consists of three to many petals (corolla).
- Calyx and corolla form the perianth.
- Several to many stamens are attached to the receptacle around the base of
the pistil.
- Each stamen consists of a filament with an anther at the top.
- Pollen grains developed and disseminated in anthers.
- Pistil consists of Stigma, Style, and Ovary.
- Superior Ovary - Calyx and corolla are attached to the receptacle at the
base of the ovary.
- Inferior Ovary - Receptacle grows up and around the ovary.
- Calyx and corolla appear to be attached at the top.
- Inflorescences - Group of several to hundreds of flowers.
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- Fruit is an ovary and its accessory parts that have developed and matured.
- Usually contains seeds.
- All fruits develop from flower ovaries and accordingly are found
exclusively in flowering plants.
- Vegetables consist of leaves, leaf petioles, specialized leaves, stems,
roots, flowers and their peduncles, flower buds or other parts of the plant
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- Fruit Regions
- Exocarp - Skin
- Endocarp - Inner boundary around seed(s).
- Mesocarp - Fleshy tissue between exocarp and endocarp.
- Three regions are collectively called the pericarp.
- Regions of a Mature Peach
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-
- Simple fleshy fruits develop from a flower with a single pistil.
- Drupe - Simple fleshy fruit with a single seed enclosed by a hard,
stony endocarp, or pit.
- Pomes - Bulk of flesh comes from enlarged floral tube
or receptacle that grows up around the ovary. (Apples)
- compound fleshy
- Berry - Usually develops from a compound ovary and often contains more than
one seed.
- True berry is a fruit with a thin skin and a relatively soft pericarp.
- Pepos - Relatively thick rinds (Pumpkins).
- Hesperidium - Leathery skin containing oils (Citrus).
-
- Dehiscent: Dry Fruits That Split at Maturity
- Follicle - Splits along one side or seam.
- Legume - Splits along two sides or seams.
- Silique - Splits along two sides or seams, but seeds are borne on central
partition exposed when the two halves separate.
- Capsules - Consist of at least two carpels, and split in a variety of
ways.
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- Indehiscent: Dry Fruits That Do Not Split at Maturity
- Achene
- Nut
- Grain
- Samara
- Schizocar
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- Derived from a single flower with several to many pistils.
- Individual pistils mature as a clustered unit on a single receptacle
- Raspberries, Strawberries.
-
- Derived from several to many individual flowers in a single inflorescence.
To learn more about this topic, you might find these sites of interest.
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- Wind Dispersal
- Small and Lightweight seeds.
- Animal Dispersal
- Seeds pass through digestive tract.
- Fruits and seeds catch in fur or feathers.
- Oils attract ants.
- Water Dispersal
- Some fruits contain trapped air.
- Mechanical Ejection of Seeds
For more information about this interesting topic, try
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The structure of a seed consists of:
- Cotyledons - Food storage organs that function as first seed leaves.
- Plumule - Embryo shoot.
- Epicotyl - Stem above cotyledon.
- Hypocotyl - Stem below attachment point.
- Radicle - Stem tip developing into a root.
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Dicot seed and seedling
-
Monocot Seed and Seedling
- To see a good diagram of the two types of seeds and read about their
germination try:
http://www.biologie.uni-hamburg.de/b-online/ibc99/koning/seedgerm.html
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- Germination is the beginning or resumption of seed growth (See
the germination process ).
- Seed must be viable.
- Some require period of dormancy.
- After Ripening
- Favorable Environmental Factors
- Viability of most seeds is significantly extended when the seeds are
stored under conditions of low temperatures and kept dry.
- A few species produce seeds with no period of dormancy.
- DORMANCY is a period of growth inactivity in seeds, buds, bulbs, and other plant organs even when
environmental conditions normally required for growth are met (p.148,217)
- Period when no growth of the embryo occurs
- Dormant seeds can survive
- freezing temperatures
- droughts
- other conditions that would kill growing plants
- not all seeds produced in a single year will germinate in the subsequent
year
- Some seeds may remain dormant for several to many years
- Mechanisms for maintaining seed dormancy
- thick, hard seed coat
- a germination inhibitor (chemical) in the seed coat or the embryo itself
and/or the lack of the necessary growth promoter
- FACTORS THAT BREAK DORMANCY:
- Environmental conditions that "break" dormancy are correlated with the
causes of dormancy
- Mechanical Abrasion:
- thawing and freezing
- Thick, hard seed coat:
- damage or break down seed coat by abrasion
- Often the dormant seeds are transported away from parent plant
- When dormancy is broken water available, if the seed coat broken
by flash flood
- damage or break down the seed coat with fire
- eliminates many competing plants
- Scarification:
- dipping in HCL
- Thick, hard seed coat:
- bird or other animal eating fruit containing the seeds can break
dormancy after the seeds transported away from parent plant and the seed
will be "planted" with "fertilizer"
- Stratification:
- placing seeds in the refrigerator for a few weeks
- In temperate environments with a winter season, inhibitors may be
degraded by prolonged cold
- Cold may also promote the synthesis or activation of growth promoters
- Imbibition: soaking them in water
- Chemical inhibitor/lack of growth promoter
- In arid environments inhibitors are leached out of the seeds by prolonged
exposure to running water
- seeds may have a hard seed coat AND chemical inhibitor
To learn more about seed germination, try these sites.
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Last modified:
October 08, 2004 by
Cynthia Herbrandson 
© Copyright 1999, Kellogg Community College.
All rights reserved.
