The dynamics of seed mortality

The shape of seed mortality curves in dry storage, and the dynamics of seed ageing are discussed as they help to define the rate-controlling processes. Emphasis is placed on distinguishing between two types of survival curves: those which show an initial period of relative stability preceding a dynamic rate of cumulative mortality, and those in which an initial period of relative stability is lacking. The fact that the survival curves had to be modelled separately for the initial plateu phase and for the sigmoid phase, support the contention that there are two phases of seed ageing. The factors operating in these two sectors are discussed and the glassy state in seeds is suggested to serve as a stabilizer, particularly as it may contribute to the period of relative stability. The rapid progress of deterioration during the dynamic period may represent a weakening of the glassy state, combined with a facile hydrolysis of sugar components and the unleashing of an array of oxidative processes. A recognition of the distinction between the period of relative stability and the period of dynamic deterioration may provide new insights about seed longevity and deterioration.