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A Handbook of Biology
ËXÅMPLËS FØR VËRÑÅLÏSÅTÏØÑ
Some food plants, wheat, barley & rye have two varieties:
SPRING VARIETIES: These are normally planted in the spring and come to
flower and produce grain before the end of the growing season.
WINTER VARIETIES: Winter varieties if planted in spring would normally fail
to flower or produce mature grain within a span of a flowering season.
Hence, they are planted in autumn. They germinate, and over winter
come out as small seedlings, resume growth in the spring, and are
harvested usually around mid-summer.`
Vernalisation in biennial plants: Biennials are monocarpic plants that
normally flower and die in second season. E.g. Sugar beet, cabbages,
carrots etc. Subjecting the growing of a biennial plant to a cold treatment
stimulates a subsequent photoperiodic flowering response.
(AIPMT Mains 2012)
SËËD DØRMÅÑÇÝ
Seed dormancy is the state in which seed is unable to germinate, even
under ideal conditions.
Mainly seed undergoes in dormant stage to protect themselves from
harsh environment.
Reason for seed dormancy
Overcoming seed dormancy
Impermeable and hard seed
coat
Man-made
method:
seed
coat barrier can be broken by
mechanical
abrasions
using
knives and sandpaper or by
vigorous shaking
Natural method: Seed coat is
broken by microbial action,
and passage through digestive
tract of animals
Presence of chemical inhibitors
such as abscisic acids, phenolic
acids and paraascorbic acid
Subjecting the seeds to chilling
condition
By applying chemicals such as
gibberellic acid and nitrates
Scarification is the artificial breaking of seed dormancy by the action of
chipping with the help of scalpel, hot water and treatment by chemicals.
When seeds are moistened and exposed for variable period at low or
high temperature, this phenomenon is called stratification.