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Literature review
initial growth of the seedling follows one of two distinct patterns (HARTMANN &
KESTER, 1965). The seedling either follows the pattern of epigeous germination,
where the hypocotyl elongates and raises the cotyledons above the ground, or
hypogeous germination, where the lengthening of the hypocotyl does not cause the
cotyledons to rise above the ground and only the epicotyl emerges (HARTMANN &
KESTER, 1965).
2.8.3 Measuring germination
It is incorrect to equate germination to seedling emergence from soil, as germination
ends sometime before this (BEWLEY & BLACK, 1994). Emergence of the axis can
however be used as a precise measurement of termination of germination (BEWLEY
& BLACK, 1994).
The progress of germination is expressed as a percentage of the total number of
seeds tested at time intervals throughout the germination period (BEWLEY &
BLACK, 1994). When this relationship is expressed graphically it ordinarily yields a
sigmoid curve. Some valuable conclusions can be drawn from variations in the shape
of such a curve. If the curve flattens off when only a low percentage of the seeds
have germinated it indicates that the seeds have a low germinating capacity
(BEWLEY & BLACK, 1994). The shape of the curve also describes the uniformity of
germination (BEWLEY & BLACK, 1994).
Mean germination time can be calculated by the following equation: MGT= (n×d) /N.
Here n=number of seeds germinated on each day, d=number of days from the
beginning of the test, and N=total number of seeds germinated at the termination of
the experiment (ELLIS & ROBERTS, 1981). When this is combined with a measure
of germination, data can be displayed in a more concise way (KULKARNI et al.,
2007).
2.8.4 Promotion and inhibition of germination
2.8.4.1 Gibberellin and abscisic acid
Numerous studies have shown that GA promotes germination in dormant and non-
dormant seeds (JONES & STODDART, 1977). It has also been shown that levels of
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