Field populations of Potentilla crantzii in the British Isles are often remarkably uniform morphologically within themselves. Purely vegetative spread seems to be very restricted, and populations consist of discrete individuals, presumably established from seed. The mechanisms involved in reproduction by seed have been investigated in three Scottish topodemes. Crosses between P. crantzii as female parent and P. tabernaemontani, P. arenaria and P. aurea as pollen plants yielded progenies which were quite uniform and which resembled P. crantzii morphologically. The mechanism of maternal inheritance in representatives of these topodemes has been elucidated cytologically. Plants from Ben Lawers and Inchnadamph differed significantly in their embryology from P. tabernaemontani previously investigated. Female meiosis was observed in all stages, but the products degenerated without exception and unreduced embryo sacs arose by diplospory. In the third topodeme from Creag an Dail, there was no sign of meiosis beyond the synapsis stage and embryo-sacs were aposporous in origin. No plants produced seed without prior pollination. Although, in emasculated flowers, the autonomous division of the egg cell formed embryos, endosperm was always lacking. The continued development of embryos is dependent on endosperm and consequently no mature seed is produced. One chromosome count in endosperm after pollination suggests that endosperm formation is the result of a genuine fertilization rather than merely stimulation by the pollen.