The mechanism of reproduction by seed in five British topodemes of Potentilla tabernaemontani has been investigated by means of crossing experiments and embryologically. With a variety of Potentilla species as pollen plants, crossing experiments yield progenies, which, except for the occasional aberrant, are uniform and resemble the female parent in morphology. Embryological preparations show meiosis to be suppressed in all topodemes. In all except one topodeme, the majority of unreduced embryo sacs are diplosporous in origin, in the other they are predominantly aposporous. Although the egg cell is capable of autonomous parthenogenetic development, functional seed is never formed without previous pollination. The conclusion to be drawn from embryology and crossing experiments is therefore that the seed produced is almost completely pseudogamous, thereby reproducing faithfully the genotype of the parent. The topodeme from Fleam Dyke, Cambridge, differed from the others investigated in a number of important respects. These included chromosome number, male sterility, the origin of unreduced embryo sacs and the precocious development of parthenogenetic embryos.