• Germination in plants is the process by which
a dormant seed begins to sprout and grow into
a seedling under the right growing conditions.
Type of Germination:
(i) Epigeal germination
– In this, the cotyledons are raised out of the soil and
generally become green and photosynthetic. In dicots, they
are pushed up by rapid extension of hypocotyl before
growth of the epicotyl.
– Epigeal germination occurs in
bean, caster, mustard, tamarind, sunflower etc.
(ii) Hypogeal germination
– In this type of germination, the cotyledons remain
underground. Hypocotyl growth is restricted. The epicotyl
grows to raise the first leaves out of the soil.
– Hypogeal germination occurs in dicotyledenous seeds of
gram, pea, mango, ground nut etc and in monocotyledons
like rice, maize, wheat etc.
Special type of Germination
(iii) Viviparous germination
– This is a special type of germination occurring in
mangrove plants. These plants generally grow in salty
lakes, sea coasts and deltas. Here, the seed germinates
while still attached to the parent plant.
– The embryo emerges out of the fruit with a massive
radicle pointing downwards. Due to increased
weight, the seedling separates from the parent plant
and establishes itself in the muddy soil below.
– Example: Rhizophora
Processes Behind Germination
Rehydration – imbibition of water.
RNA & protein synthesis stimulated.
Increased metabolism – increased respiration.
Hydrolysis (digestion) of food reserves by
(e) Changes in cell ultrastructure.
(f) Induction of cell division & cell growth.
(a) Rupture of seed coat.
(b) Emergence of seedling, usually radicle first.
POST GERMINATION (a) Controlled growth of root and shoot axis.
(b) Controlled transport of materials from food
stores to growing axis.
(c) Senescence (aging) of food storage tissues.
Factor Affecting on Germination
1. Abiotic Factors:
3) Aeration (Oxygen)
4) Soil type and depth of sowing
2. Biotic factors:
1) Viability of seed
2) Dormancy period
3. Other factors:
• Factors that affect seed germination are
divided in two categories, internal and
• The internal factors include seed vitality,
genotype, seed maturation and seed
• The external factors are: water, temperature,
oxygen, light and smoke.
Abiotic Factors: LIGHT
• Generally seeds require darkness to germinate.
However, lettuce, tobacco, tomato and many grasses
need to light exposure to germinate.
• These seeds require the red portion of the light
spectrum, while far red light inhibits germination.
Many small seeds with low amounts of storage
reserves (such as lettuce) show such a red light
• These seeds must not be buried below the soil so deeply
that light cannot penetrate. Although research suggests
that even a few minutes of exposure will allow the
germination to occur.
• Phytochrome is a plant pigment found in cytoplasm
that senses the presence of red light. The red-absorbing
form of phytochrome changes to the far-red absorbing
form when it absorbs red light (660 nm) and back again
when it absorb far-red light (730 nm). Thus the
presence of the far-red form of phytochrome ends the
inhibition of germination in these seeds.
Abiotic Factor: Temperature
• As with most reactions germination generally occurs
faster when at warmer temperatures. However there is
sometimes a need for cool temperatures to break
• Stratification is one strategy that is employed in
woody species in particular. It requires a moist, cool
period that degrades growth inhibitors that prevent
germination. Once the inhibitors are degraded and all
other conditions are met then germination will occur.
• The temperature for germination to occur is quite
different than the temperature requirement to break
dormancy. Generally the temperature for
germination correlates to the temperature needed
for successful plant growth.
• Seeds of cool season crops germinate best at
temperatures between 32 and 50 degrees
Fahrenheit. (Examples: celery, lettuce, peas.) Warm
season crops germinate best at temperatures
between 59 to 79 degrees Fahrenheit.
Abiotic Factors: Oxygen
• Another requirement for germination is aeration
• A. Respiration rates for germinating seeds are
very high, therefore adequate oxygen is necessary.
The germination percent of most seeds will be
retarded if the oxygen percent goes below 20
percent. (Normal air is 20 percent oxygen.)
• B. Seedbeds that are over-watered or poorly
drained will cause the oxygen supply to become
limited, so the germination percent will diminish.
Abiotic factor: soil type
• Soil type is widely affected on seed
germination, there are so many parameters of
soil affecting on seed germination.
• In that factors, soil salinity, acidity, salt
concentrate, EC of soil, soil porosity, water
holding capacity, texture of soil also affect on
seed germination. Most problematic factor is
water holding capacity of soil water holding
Abiotic factor: Depth of sowing
• Proper planting depth is a direct correlation to seed
• The general rule of thumb is larger seeds can be
planted more deeply than small seeds. This is due to
the energy needed to emerge. Larger seeds have
greater food reserves from which to draw energy for
respiration and growth. They are able to emerge from
• Soil types also affect the planting depths. The surface
of sandy soils tends to dry out quickly, so seeds planted
in these soils should be planted deeper, than in loam
• Most seeds produced by mature plants pass
through a period of inactivity or dormancy
prior to germination. During this period of
inactivity, seeds remain viable.
• Dormancy may be internal, external, or a
combination of both.
Embryo (Internal) Dormancy
• Dormancy may occur when a mature seed contains
an underdeveloped or immature embryo.
• Internal dormancy of most seeds involves a period of
after-ripening. After-ripening occurs when a seed
does not or is not ready to germinate until it
completes a certain stage of development.
• Some seeds mature in the fruit but do not germinate
until released from the fruit.
• This type of dormancy can not be overcome, it can
be only recover by waiting till seed become ready.
Seedcoat (External) Dormancy
• A seed may require a certain amount of light to
germinate causing the seed to remain dormant until
exposed to light.
• The seed coat may be hard and/or thick, preventing
the absorption of water, intake of oxygen, or physically
preventing the expansion of the embryo.
• This type of dormancy can be recover by scarification.
By scarification we can make seed coat soft and thin for
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