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A randomly-drawn sample of 51 plants from a natural population (R106) carried between them 31 different S-alleles whose frequencies were, contrary to theoretical expectation, significantly unequal. Two alternative hypotheses are proposed to account for this unexpected observation. One of the eleven S3 alleles found in the experiment appeared to be a stigma part mutant of the revertant type.

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SUMMARYThough the self-incompatibility polymorphisms are as well-known as any and have been the subject of much theoretical investigation, little is known about their characteristics in natural populations.A preliminary survey of the extent of the polymorphism in P. rhoeas found 32 different S-alleles among eighteen full-sib families derived from natural populations growing in three widely separated localities in the West Midlands. Though most of these a'leles occurred in one or other of these populations only, an analysis of their distribution between localities failed to show any significant differentiation between them.These results are compared with those from other species and reasons are given for the apparent lack of differentiation between localities.