10 - plant reproduction
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PLANTREPRODUCTION
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THE FLOWER
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THE FLOWER
A branch stem bearing leaves which are specialized
to carry on reproduction.
A leaf that surrounds a flower
may be an ordinary leaf or
bracteole.
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Bracts surround or enclose a flower
cluster
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Flower stalka stem which supports the flower in afavorable position for pollination.
When it bears a single flower or a cluster of flowers it is knownas a peduncle.
In a flower clusters the individual stalks are termed as
pedicles.
.
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The Parts of a Typical Flower
1. Perianth or the Floral Envelope made up of the
following parts:
a. Sepals (collectively called calyx)
* protects the inner parts of the flower
before the bud opens
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b. Petals (collectively calledcorolla)
* to attract insects as agent of pollination
Nectariessugar secreting glands
Ethereal oilsaromatic odors
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Petals
Two parts:
a. laminaflattened showy portion
b. claw
posterior constricted partattached to the receptacle
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A. Stamen
Male reproductive part of the flower
Collectively constitute the androecium
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Parts of the stamen:
A. filament a stalk which supports the anther
B. anther contains pollen sacs within which pollen grains
are formed.
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B. Pistil
Collectively constitute the gynoecium
female reproductive structure.
Parts:
* ovary
contains the ovules in a cavity called locule
* style - stalk arising from the ovary
* stigma
tip of the style
Each unit of the pistil is a called carpel.
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Types of Flower
A. According to the presence or absence of somefloral parts:
1. Complete flowers
all floral parts arepresent (perianth and essential)
2. Incomplete missing floral parts
a. apetalous missing petals
b. naked
if both perianth parts are absent
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B. According to sexuality:
1. Perfect flowers both stamen and pistil
are present.
2. Imperfect flowers if only stamen or
pistil is present.
* Staminate or male flower
* Pistillate or female flower
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C. Accdg. To the presence of essential parts:
1. Monoecious if pistillate and staminate
flowers are produced in the same individual
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2. Dioecious pistillate and staminate flowers
are found in separate individuals
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Physiology of the Flower
Environmental factors that control theflowering of angiosperms:
1. Photoperiod
response of plants tolength of day.
2. Temperature
3. Moisture
4. Soil nutrient
5. Amount of crowding
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Groups of plants based
on photoperiodism:
1. Short-day plants or Long-night plants those
which flower only if the day length is reduced
below a certain critical value.
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2. Long-day plants or Short-night plantsthose
which flower only if the day length exceeds a
certain critical value
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3. Day-neutral plantsbear flowers upon reaching a
certain age or size, irrespective of day length.
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Temperature
Many flowering plants are dependent upon
exposure to very low temperature while
others require high temperatures.
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Vernalization
Is the cold treatment of germinating seeds in
order to hasten subsequent flowering.
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Kinds of pollination:
1. Self-pollination transfer of pollens from
stamen to the stigma of the same flower or
individual or between flowers of plants of the
same genetic characteristics.
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2. Cross-pollination transfer of pollens from
the stamen to the stigma of another flower or
between plants of different geneticcharacters.
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Agents of pollination:
Insects insect pollinated flowers arecalled entomophilous.
Wind wind pollinate flowers are calledanemophilous.
Animals
Man
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Characteristics of insect pollinated
flowers:
* Large, brightly coloredpetals
* Often sweetly scented
* Usually contain nectar
* Moderate quantity of
pollen
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* Pollen often sticky
or spiky
* Anthers firm and
inside flowers
* Stigma are located inside
the flowers
* Stigma has sticky coating
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Characteristics of wind pollinated flowers:
* Small petals, often brown or dull green
* No scent
* Pollen produce in
great quantities
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* No nectar
* Pollen very light and smooth
* Anthers loosely attached
and dangle out
* Stigma hangs outside the
flower
* Stigma feathery or net like
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FRUITS
A mature ovary of a flower
including its one or more
seeds and any part of a
flower which may be
closely associated with
the matured ovary.
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The ovary wall thickens and ripens into
the pericarp.
Three distinct parts of pericarp:
a. exocarp
outermost part (skin)
b. mesocarp middle part
c. endocarp innermost part
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Seeds
Seeds are mature ovules.
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Parts of the seed:
1. Embryorudimentary plant which develop from thezygote.
2. Endospermdevelops from the daughter nuclei of theendosperm nucleus and serves as food storage tissue.
3. Seed coatdevelop from the integuments of the ovule.
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Layers of the seed coat:
a. Testaouter seed coat derived from the
outer integument of the ovule which is
usually hard.
b. Tegmeninner coat derived from the inner
integument which is usually thin filmy
membrane.
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External features of th seed coat:
a. Hiluma scar which
marks the place where
the seed broke off from
the stalk (funiculus)
b. Raphea ridge formed
by the stalk of the ovuleand present only in ovules in which thefuniculus is sharply bent at the base of theovule.
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c. Micropylemicroscopic pore of the seed.
d. Chalaza
the region at the upper end of theraphe opposite the micropyle where the
funiculus spreads out and unites with the base
of the ovule (proximal end of the seed)
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Seeds