His aim will not be accomplished by one crossing. Connecting links are required, and therefore the North American beach plum has to be crossed with other American and Japanese plums (Prunus triflora and P. Americana), and each of these hybrids with four or five kinds of the common plum. Finally a series of hybrids is developed from which almost anything can be expected.
It is natural that by such crossing we must expect the appearance of undesirable characters as well as desirable ones. Some plants produce only good, others only bad, characters, but the greater part exhibit some good points in connection with a larger or smaller number of undesirable qualities. From hundreds of thousands only those must be selected which possess all the desired characters. To make this possible it is necessary not only to cross six or eight kinds with one another, but to use as many sub-species and varieties as possible for the experiments. This work necessitates hundreds and even thousands of experiments. The result of each crossing can only be judged by the fruit, and this indicates new combinations. It can easily be seen what an immense amount of work, patience and capacity of judgment and choice is required to reach the ultimate aim. Yet Burbank told us on that remarkable evening of many such instances. He was enthusiastic in his hope to be able to realize all this during his life.
The making of hybrids from the different species of plums naturally brought us to a subject which, for me, was of the greatest importance from a scientific standpoint. As Arrhenius and Loeb also felt more interest in the theoretical side of these problems, I took the first opportunity to bring the conversation to that point.
I had in mind the 'pitless prune.' Just imagine this, reader! Next day Burbank took us to a plum tree heavily loaded with clear blue, very attractive, yet small plums. He picked a few and asked us to bite right through the middle of the fruit. We did as requested, and although we knew there was no stone in the plum, we experienced a feeling of wonder and astonishment. Inside the plum was a seed, like an almond in its shell, and with the taste of an almond, but without the stony covering. When cutting through the fruit, we found the seed surrounded by the green fruit-flesh, the innermost part of which was a jelly-like mass, in which could yet be seen some remnants of hard little stones, that scarcely offered any resistance to the knife. Burbank declared, however, that he was not at all satisfied with the result, and said that he had already young trees with fruits, in which nothing could be detected of the stone.
Osterhout told us about the impression this plum made on Professor Bailey, professor of agriculture at Cornell University. He came unprepared before this tree, and Burbank, always full of humor, thought it a good opportunity to play a little trick. Bailey had declared that
