Summary 1.We investigated the vertical distribution of seeds in the soil, using data from nine studies in five European countries. We discovered significant correlations between seed shape and distribution in the soil. 2. The classification of the longevity of seeds of plant species has been improved by the introduction of a 'longevity index', expressing on a continuous scale the most recent information on seed longevity represented as the proportion of non-transient seed bank records in the database of Thompson et al. (1997). Remarkably, no difference in seed longevity was found if the index was based on direct observations only when compared with the index based on the complete data set where indirect, 'depthderived' observations were included. 3. Seed longevity was best estimated using a multiple regression model with an integrated measure of seed size and shape and depth distribution of seeds. 4. The shape of seeds, known to be a consistent character of species, was shown to be constant within species, whereas depth distribution of seeds was highly variable among sites. This is consistent with the variability of seed longevity found in published seed bank data.

Germination in light and darkness was compared after cold stratification of seeds of 54 species known or suspected to accumulate persistent seed banks. Germination became less dependent on light with increasing seed mass. This pattern was clear in a direct correlation of individual species data (P<0.0001) as well as when considering phylogenetically independent contrasts (P<0.001). The latter analysis suggests that light response and seed mass coevolved.

No abstract

Variation in dormancy level was tested in seeds of four species, each collected from three populations in 1994 and 1995 (experiment 1) Germination was tested in light and darkness on recently-harvested seeds and on those after-ripened in dry storage for one year In addition, seeds from each of eight individual plants within each of eight populations were tested for germination when recently harvested and after warm stratification or cold stratification followed by a drying period (experiment 2) Seeds from the two years differed in dormancy level in Silene noctiflora, Sinapis arvensis and Spergula arvensis Germination percentage differed significantly among populations in Sinapis arvensis and Spergula arvensis in both experiments and in Thlaspi arvense in experiment 2 Furthermore, dormancy level in seeds from different mother plants also varied in the three species tested in experiment 2 Variations at the three levels tested (year, population and mother plant) indicate that these species have a random pattern of variation in dormancy level It is concluded that variation in seed dormancy among mother plants, populations and years must be taken into account when testing the germination characteristics of a species and also when attempting to model weed seed bank dynamics

No abstract