Experiments on the genetics of wild populations

Abstract

1. The British distribution ofP. maritima is continuous throughout the coastal regions, but is localised inland. 2. The species is an aggregate of many growth-forms representing various combinations of characters. Growth habit ranges from the decumbent to the erect form, and five types have been described and figured. 3. Plants derived from a single area on the east coast of Scotland were studied. This locality, though very limited in extent, was ecologically divided into two regions: (a) an exposed rock habitat; and (b) an adjoining grassy slope. 4. Although the two habitats were not spatially isolated, population differentiation had occurred. 5. In the wild, the environment had modified both populations considerably, but the effect was more marked in the case of the rock population. 6. In culture the rock populations possessed a larger proportion of low-growing forms than did the grass population, but the latter contained no classified type which was not also present in the former. 7. A phenotypic parallelism between the modificatory effect of the environment on the populations in the wild and the growth-forms present in the cultured populations was observed. 8. It is possible that occasionally the phenotypical characteristics of growth-forms determine their survival, and some importance should be attached to the value of the several genotypes represented by a particular plienotype.