“…Firstly, while the number of alleles in populations of Trifolium pratense (Williams & Williams, 1947;O'Donnell & Lawrence, 1984) and T repens (Atwood, 1944) appear to be large, this number appears to be much smaller in the two most thoroughly investigated species with a one-locus, multi-allelic, gametophytic system of self-incompatibility. Thus Emerson (1940) found 45 different S-alleles in Oenothera organensis and we have found, quite coincidentally, the same number in P. rhoeas. Furthermore, only 49 different S-alleles have been found in Brassica oleracea (Ockendon, 1985), which is the most extensively investigated species with a one-locus, multiallelic, sporophytic system of self-incompatibility.…”