The goal of this article is threefold: First, the theoretical background for a model-based framework of argumentation to describe and evaluate argumentative processes in science education is presented. Based on the general model-based perspective in cognitive science and the philosophy of science, it is proposed to understand arguments as reasons for the appropriateness of a theoretical model which explains a certain phenomenon. Argumentation is considered to be the process of the critical evaluation of such a model if necessary in relation to alternative models. Secondly, some methodological details are exemplified for the use of a model-based analysis in the concrete classroom context. Third, the application of the approach in comparison with other analytical models will be presented to demonstrate the explicatory power and depth of the model-based perspective. Primarily, the framework of Toulmin to structurally analyse arguments is contrasted with the approach presented here. It will be demonstrated how common methodological and theoretical problems in the context of Toulmin's framework can be overcome through a model-based perspective. Additionally, a second more complex argumentative sequence will also be analysed according to the invented analytical scheme to give a broader impression of its potential in practical use.

Seed dormancy was analysed in Geraniaceae, testing 29,103 seeds of 35 species for seed-coat impermeability to water. Seeds of wild and cultivated species from a number of different climatic/ecological zones (northern Germany, the Canary Islands and South Africa) were investigated. Seeds from cultivated plants and natural populations had similar (±2%) percentages of water-impermeable seeds. The percentages of impermeable seeds at maturity were also mostly constant (±2%) for two different years. The species analysed contained from 0 to 100% impermeable seeds at maturity, and could be classified into three quantitative types of physical dormancy: four species with no impermeable seeds (PY0), 10 species with a maximum of 80% impermeable seeds (PY80), and 21 species with more than 80% impermeable seeds (PY100). Species with different life cycles and from very different habitats, e.g. Geranium pratense or Pelargonium capitatum, belonged to the PY100 group. However, all of the succulent shrubs investigated from the genus Pelargonium were PY0 species. Five years of dry storage at 20 ± 5°C decreased physical dormancy in a species-dependent fashion. Erodium cicutarium, for example, had 95% impermeable seeds at maturity; all of them became permeable during the dry storage and began to germinate immediately after placing them on a moist substrate. Physical dormancy of other species, e.g. Pelargonium zonale, Pelargonium vitifolium or Geranium pratense, was not affected by dry storage. Thus, physical dormancy is a diversely differentiated feature in Geraniaceae with regard to both percentages of impermeable seeds at maturity and maintenance of dormancy under particular conditions.

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