10 - Plant Reproduction

7/29/2019 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

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10 - Plant Reproduction