Some English Walnuts
Mr. Burbank's Paradox walnuts very closely resemble the English walnuts shown here, but instead of having thin paper shells like these, they have the thick, woody shell of the black walnut. The Paradox, however, was not selected as a nut-bearing tree, but as a quick-growing lumber tree. It produces very, few nuts, in fact, but such as are produced will germinate readily if planted.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 2 Chapter 5