These potatoes were grown on roots on which a tomato top was grafted. The tomato leaves have supplied material for the unwonted purpose of making potatoes, but the product is of a dwarfed and perverted character. When the potato vine is grafted on the tomato roots, no potatoes are grown underground, but they may grow from the axils of the leaves in the air, as shown in some of Mr. Burbank's early experiments.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 2 Chapter 9