There are a good many species of wild grapes, and Mr. Burbank has utilized several of these in his experiments. His chief work with this species has been done, however, with the common European cultivated grape, which has developed a large number of varieties through being selected for various purposes during past centuries. In particular some of his most important new varieties are descended from a "bud sport," that is, a variation that appeared "spontaneously" in a branch growing on an ordinary grape vine.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 3 Chapter 7