Representing Cumulative Germination.: 2. The Use of the Weibull Function and Other Empirically Derived Curves

Abstract

The Weibull, Morgan–Mercer–Flodin, Richards, Mitscherlich, Gompertz and logistic functions were each fitted to a wide range of cumulative germinations of non-dormant seed. The Weibull proved the most suitable for describing cumulative germination as it provided a consistently close fit to the data and was insensitive to choice of starting values, thus making it fairly easy to fit. The others provided either an inferior fit or else a similar fit but with a greater sensitivity to starting values.The four parameters of the Weibull function reflect maximum germination, germination rate, the lag in the onset of germination and the shape of the cumulative distribution.A comparison between non-linear and linear fits of the Mitscherlich, Gompertz and logistic functions showed the clear superiority of non-linear methods.