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The germination-time curves for a series of experiments at constant temperatures and osmotic potentials were analysed to produce a relationship between germination, time, temperature and osmotic potential. The analysis involved the concept of hydrothermal time which is a combination of potential above a base potential, temperature above a base temperature and time. For most of the population of sugar-beet seeds examined, the hydrothermal time required for germination was constant. The base temperatures of the seeds were similar but the base potentials varied between seeds. Analysis of the times to germination of fractions of the seed population, grouped according to the order in which they germinated, showed that the base potentials were almost normally distributed An equation using this distribution can be used to predict the time course of germination over a wide range of temperatures and potentials. The equation uses five parameters to describe a seed population: the proportion of live seeds, the hydrothermal time required for germination, the base temperature and the mean and standard deviation of base potential.
R. J. Gummerson (Wed,) studied this question.