In Europe and the Near East, clinal variation manifests itself in the glycoside concentration of the leaves of Trifolium repens . Occurrence and distribution of the corresponding genes correlate strongly with the 0 C January isotherm. Other legumes display comparable differences. As in the case of Lotus corniculatus , a temperature-dependent distribution of varieties containing glycoside correlates with the distribution of certain snail species sensitive to the cold. Whether, however, the distribution of its feeder is indeed the cause for the distribution patterns of the legumes glycoside genes has still to be proven.
Polymorphism is, as has been discussed before , a typical feature of cultivars.
The advantage of the successful variety is strictly limited to the environmental site conditions of the habitat, where it is grown. Harvested seeds were partly used for further mixed cultivation and partly for assaying. A falsification of the results due to hybrid formation was ruled out, since self-fertilization is typical for Hordeum vulgare . The results of a typical count are shown here.