Heterosis resulting from degenerative changes.

ERITABLE variations in inbred strains of maize occur infrequently. All H the mutations BO far found either do not increase the amount of growth and productiveness or clearly reduce the plants in some degree (JONES 1924, 193a, 1944; SINGLETON 1943). Several changes have been noted recently and reported in a preliminary way (JONES 1944) which reduce the vigor of the inbred plants but which increase the growth of their hybrid offspring when they are crossed back to the normal line from which they were derived and from which they differ by what appears to be a single allele. These mutations and their effects in hybrid combinations are described ip detail here.