DIFFERENCES in length of tuber dormancy which are related to mineral content have been found during work on the effect of the mineral nutrition of the potato plant on the performance of its progeny. To relate these differences to tuber biochemistry, it was necessary to know the effect of tuber extracts on the dormancy of whole tubers. Previous attempts to control dormancy by treating potato pieces with either tuber peel extracts containing the inhibitor-β complex1 or with one of its components, abscisic acid, have failed2, although the disappearance of this complex from the tuber has been correlated with the breaking of dormancy3. It is also known that cutting a tuber causes a wound reaction which leads to the breaking of dormancy4. Furthermore, the practice of soaking tubers in concentrated solutions for up to 24 h produces anaerobic conditions which could have effects on dormancy as great as those of the extract being supplied.