The germination-time curves for a series of experiments at constant temperatures and osmotic potentials were analysed to produce a relat10nship between germination, time, temperature and osmotic potential. The analysis involved the concept of hydrothermal lime which is a combination of potential above a base potential, temperature above a base temperature and time. For most of the population of sugar-bee t see ds examined, the hydrothermal time required for germination was constant. The base temperatures of the seeds were similar but the base potentials varied between seed s. Analysis of the times to germination of fract10ns of the seed population, grouped according to the order in which they germmated, showed that the base potentials were almost normally distributed An equation using this distribution can be used to predict the lime course of germination over a wide range of temperatures and potentials. The equation uses five parameters to descnbe a seed population: the proportion of live seeds, the hydrothermal lime required for germination, the base temperature and the mean and standard deviation of base potential.

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SummaryExperiments are described in which a range of seed beds was created in each of 5 years. The weather in these years produced wet, dry and capping seed-bed conditions. The time course of sugar-beet seedling emergence on each seed bed was recorded each year and the differences were considered in terms of soil physical characteristics: much of the year-to-year variation was accounted for by considering thermal time above 3 °C. The differences in emergence between seed beds were large only when conditions were dry, but in all years it was advantageous to level the seed bed in autumn or winter. Seed beds with a dense soil below the seed and fine aggregates above gave the most suitable conditions for rapid and successful emergence.