The paradox walnut hybrid—Juglans hindsii x J. regia—is very much in demand by California walnut growers as a rootstock for English walnut varieties due to its vigor and its resistance to crown rot—Phytophthora cactorum—tolerance of excess water, and apparent potential resistance to root lesion nematodes—Pratylenchus vulnus. Such hybrid seedlings are ordinarily obtained from nuts taken from Northern California black walnut—J. hindsii—trees growing in the vicinity of English walnut—J. regia—trees. Since the individual seedlings vary considerably in their vigor and in their resistance to various diseases and nematodes, it would be very desirable to be able to propagate such rootstock trees vegetatively from outstanding selected hybrid parent trees. However, cuttings of these hybrids have been extremely difficult to root and at present vegetative propagation is limited almost entirely to trench layering.

California Agriculture, May 1956, page 7, published a description of mist equipment.