Vegetative Hybridization

the phenomenon of the mutual influence of the stock and scion upon each other during plant grafting. Numerous examples of mutability during grafting, when one kind of plant was under the influence of another, are given in the works of C. Darwin, L. Burbank, and others. The mutual influence of graft components was widely used by I. V. Michurin for the development of new kinds of fruit-bearing plants. However, the mutual influence of the stock and the scion, no matter how varied it may appear outwardly (changes in the vegetative duration, blooming period, resistance to cold, growth intensivity, and so forth) may be traced mainly to changes in the nourishment of both symbionts—that is, it has the character of a modification. The basic specific species characteristics do not, as a rule, change during “vegetative hybridization,” no matter how long the influence of one component on another has been. “In this respect the stock and the scion preserve in full the individual particularities belonging to them. To date, not a single authentic instance is known where the influence of the stock on the scion could have been passed on through inheritance in sexual reproduction” (N. I. Vavilov, “Ocherk ucheniia o transplantatsii [privivke] rastenii,” Sad i ogorod, 1916, vol. 32, nos. 2-3, p. 59).

Genotypic (inheritable) changes of separate characteristics during grafting are rarely observed. They arise as a result of mutation, which is caused by traumatization of the plant during grafting. In this traumatization the stock (or scion) can, through its specifics, influence the character of the mutation. Thus, assertions that each grafted plant produces in its descendants from seeds “vegetative hybrids” not distinguishable in principle from sexual ones and that any characteristic can be passed on by means of grafting, just as by sexual reproduction, do not correspond to reality.