In Europe the commercial varieties of Asiatic walnut (Juglans regia) are referred to simply as walnuts. But in the United States they are called English walnuts or Madeira nuts. The varieties from west Europe do not prove hardy in tree, except at a few points in the Middle States, and in many places where the tree is hardy they fail to bear nuts profitably. Near the seacoast, from New Jersey southward to Georgia, the nut has been profitably cultivated for home use and market for many years. In Florida and the Gulf States it has not been favorably reported, mainly on account of the root-knot. On the Pacific slope the tree is hardy in north California, but as yet varieties have not been found that have borne nuts in a regular and profitable way. In south California, in fertile valleys where water is permanent by seepage from higher irrigated levels, within ten feet of the surface, in Santa Barbara, Los Angeles, and Ventura counties, walnut orchards are proving profitable and the acreage is rapidly increasing. With increased experience, commercial growers now intermingle varieties in orchard planting, even including trees of the native black walnut, to supply pollen. It may prove that lack of pollination is a main cause of failure to perfect fruit in many places where the trees are hardy enough to be used for shade. Luther Burbank, of Santa Rosa, California, is a close observer. He says: "Walnut-trees thrive and grow in Sonoma County, but fail to produce nuts, except a tree here and there. I discovered the reason in 1890 and fully confirmed it in 1891. Most of the trees in this section are pistillate, and, with one or two exceptions, they are strictly so. Another reason with some nut trees is that staminate flowers appear too early, or too late to bo of service to the pistillate flowers. This is a very important matter in nut culture."
Where walnut-growing is now systematized by commercial planting, alternating varieties is practised. It may prove that in many places where the trees prove hardy but unfruitful, that as yet no attention has been given to the important question of pollination.