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In editing the reply by Stephen C. Fry of the University of Edinburgh, UK, to the question: “What factors determine the point on the surface of an apparently homogenous potato at which a new sprout bursts forth?” (26 May), we introduced a note of ambiguity. While the botanical definition of a stem is that it is a structure with “a bud … between the stem and each leaf or branch”, the latter does not apply in the case of a potato. Sorry.