The bitter spongy husk deters the squirrels from gnawing into the nut until the husk is dry and brittle. Hidden in the ground, the shell absorbs moisture, and winter frost cracks it, by the gentle but irresistible force of expanding particles of water as they turn to ice. So the plantlet has no hindrance to its growth when spring opens.
Imitating nature, the nurseryman lays his walnuts and butternuts in a bed of sand or gravel, one layer above another, and lets the rain and the cold do the rest. In spring the "stratified" nuts are ready for planting. Sometimes careful cracking of the shell prepares the nut to sprout when planted.
The Japanese walnuts (J. Sieboldiana and J. cordiformis) are grown to a limited extent in states where the English walnut is not hardy. They are butternuts, and very much superior to our native species. A Manchurian walnut has been successfully introduced, but few people but the pioneers in nut culture know anything about these exotic species. South America and the West Indies have native species. So we shall not be surprised, in our travels, to find walnuts in the woods of many continents.
The English Walnut
J. regia, Linn.
Originally at home in the forests of Persia and northwestern India, the English walnut was grown for its excellent nuts in the warm countries of Europe and Asia. It was a tree of great reputation when Linnaeus gave it the specific name that means royal. Indeed, this is the tree which gave to all the family the name "Juglans," which means, "Jove's acorn," in the writings of Roman authors. Kings made each other presents of these nuts, and so the range of the species was extended, even to England, by the planting of nuts from the south.
It became the fad of gardeners, before the fifteenth century, to improve the varieties, and to compete with others in getting the thinnest shell, the largest nut, the sweetest kernel, just as horticulturists do now. In 1640 the herbalist Parkinson wrote about a variety of "French wallnuts, which are the greatest of any, within whose shell are often put a paire of fine gloves, neatly foulded up together." Another variety he mentions "whose shell is so tender that it may easily be broken between one's fingers, and the nut itsself is very sweete."
In England, the climate prevents the ripening of the fruit of walnut trees. But the nuts reach good size, and are pickled green, for use as a relish; or made into catsups—husks and all being used, when a needle will still puncture the fruit with ease.
In America, the first importations of the walnuts came from the Mediterranean countries, by way of England, "the mother country." In contradistinction to our black walnuts and butternuts, these nuts from overseas were called by the loyal colonists "English walnuts," and so they remain to this day in the markets of this country.
It was natural and easy to grow these trees in the Southern states. But little had been done to improve them, or to grow them extensively for market, until California undertook to compete with Europe for the growing American trade. Now the crop reaches thousands of tons of nuts, and millions of dollars come back each year to the owners of walnut ranches. Hardy varieties have extended the range of nut-orcharding; and so has the grafting of tender varieties on stock of the native black walnut of California.