COMPARATIVE BIOLOGY OF TUSSILAGO FARFARA L., CHAMAFNFRION ANGUSTIFOLIUM (L.) SCOP., EPILOBIUM MONTANUM L., AND FPILOBIUM ADFNOCAULON HAUSSKN.

S ummary This paper describes the results of experiments on the growth of Tussilago farfara, Chamaenerion angustifolium, Epilobium montanum and E. adenocaulon in glasshouse conditions and also results of field experiments with Chamaenerion angustifolium and Epilobium adenocaulon . These results and results of work on germination, reported in the previous paper of this series, are discussed in relation to the ecology of the species. Glasshouse experiments showed that the growth forms of Epilobium montanum and E. adenocaulon are under the control of daylength but the growth form of Chamaenerion angustifolium is not controlled by it. All four species were found to make adequate growth under a range of shade conditions and nutrient supply. In all four species, plasticity of form of adaptative significance was shown to occur with respect to both light and mineral nutrient supply. Certain attributes of the species appear to be of high significance in determining, under natural selection, their ecological distributions. These include the longevity of dormant seed and the efficiency of dormancy mechanisms. Differences in these between the species appear to lead to differences in their occurrence in deciduous woodland and in their occurrence as weeds of cultivated ground. The small seed size of the species together with their commitments to large amounts of seedling growth relative to seed weight, operate to restrict seedling establishment to open sites in which supplies of light and mineral nutrients are adequate. The growth commitments of C angustifolium appear to be appreciably larger than in the other species and in C. angustifolium seedling establishment was found to be restricted by the nutritional status of certain experimental sites to a greater extent than in Epilobium adenocaulon . Differences between the species in growth form and pattern of vegetative reproduction appear, in part, to account for the differences in their occurrence in sites with mobile soil surfaces and in closed communities. The species differ in capacity for germination and viable growth on acid substrates. Also, between the species there are differences in their growth in regimes of high calcium/low potassium concentrations. Both these differences are considered to be of importance in determining respective differences of distribution of the species on acid and on lime‐rich soils. Finally, some assessment is made of the relative importance of genetic diversity and phenotypic plasticity to the survival of the species in the wide ranges of habitats in which they occur. The importance of differences in breeding system in maintaining different levels of diversity in the species is discussed.