The Contribution of Autecological and Genecological Studies to Our Knowledge of the Past Migrations of Plants

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Abstract
Four stages, any one of which may be crucial in the life-history of a plant, are listed; vegetative growth; flowering and seed-formation; dispersal of propagules to suitable sites; re-establishment, either in the same station or in a new one. By seeking out the crucial stages, and discovering how the environmental factors controlling them have varied in the past, valuable information may be obtained concerning the history of the taxa involved and, possibly of the floristic elements which include them. Illustrations are given bearing on the histories of the Lusitanian element and plants of open places (expecially weeds) in the British flora; the world-distributions of heterostylous and homostylous species in a number of genera, particularly Primula. A correlation between homostyly and establishment after "long-distance" dispersal appears to be establishable and this is used to show that immigration of taxa from Eurasia to North America by the Bering Strait route has been accomplished much more easily than across the Atlantic Ocean. Heterostyly has been preserved in the former case; in the latter only homostylous species have been successful.