Sketch of the Evolution of our Native Fruits p. 202-203 (1898)
Liberty Hyde Bailey

Wild Goose plum x Peach

An interesting peculiarity of the Wild Goose plum is the facility with which it appears to hybridize with the peach. The most famous instance of such apparent hybridization is that of the so-called Blackman plum. About thirty years ago, Mrs. Charity Clark procured from an orchard in Rutherford county, Tennessee, which contained Wild Goose and Washington plums, seeds of plums, and gave them to Dr. Blackman, of Nashville. One tree among the resulting seedlings bore good fruit, which was called the Blackman, and was disseminated by a local nurseryman. A competing nursery, in endeavoring to procure cions from this tree, inadvertently cut them from an adjacent tree—itself one of the batch of seedlings—and sold the trees which it grew as Blackman. Now, this second tree makes fruit-buds in abundance, but they never open; and from the resemblance of the leaves to those of the peach, the plant is generally thought to be a hybrid between the Wild Goose and the peach. Curiously enough, the genuine Blackman has never been widely disseminated, but the spurious and worthless substitute has been sold in large quantities. In order to avoid confusion, the original Blackman has been rechristened Charity Clark. There are, therefore, two Blackman plums, one of which is practically unknown to cultivation, but which has been renamed, and the other is barren and will soon pass from sight.

The only authentic hybrid which has come from the union of the Wild Goose and the peach has been produced by J. W. Kerr, of Maryland. Mr. Kerr's tree, as I recall it, is large, spreading and peach-like. The leaves are long and peach-like, although rather broad and short-pointed, but the flower-buds, although they form in profusion, never open, so that the tree is barren. This is a hybrid between the Wild Goose and Troth's Early peach. Twenty-five flowers of Wild Goose were emasculated in the bud and covered with paper sacks. When in full bloom, peach pollen was applied, but the flowers were not again covered. Twenty-one of the flowers set fruit, and twenty-one trees were obtained from the seeds. Twenty of the trees were indistinguishable from peach, but the remaining one, as indicated above, gives every evidence of being an intermediate.

Brown: Form and Structure of Certain Plant Hybrids in Comparison With the Form and Sructure of their Parents (1913)

A hybrid between Wild Goose Plum and Troth's Early Peach showed that segregation had advanced a step farther; whole patches of epidermal cells of the twigs were exactly like the epidermal cells of either parent.