Experiments on the genetics of wild populations

Summary

• 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.