alleopathic chemicals, and rodent-dispersed seeds, have also contributed. The nuts are food for many rodents and make up to 10% of the diet of eastern fox squirrels. The nuts are also eaten by species of birds. The leaves are browsed by white tailed deer, although they are not a preferred food. Squirrels also eat the nuts. Where the range of the eastern black walnut overlaps that of the Texas black walnut (J. microcarpa), the two species sometimes interbreed, producing populations with characteristics intermediate between the two species. J.nigra and J. cinerea often grow in the same range as well but they do not hybridize naturally. The tree's roots often form endomycorrhizal relationships with fungi in the genus Glomus. Some endomycorrhizal relations improve the plant's growth. Species often associated with J. nigra include yellow-poplar (Liriodendron tulipifera), white ash (Fraxinus americana), black cherry (Prunus serotina), basswood (Tilia americana), American beech (Fagus grandifolia), sugar maple (Acer saccharum), oaks (Quercus spp.), and hickories (Carya spp.). Near the western edge of its range, black walnut may be confined to floodplains, where it grows either with American elm (Ulmus americana), common hackberry (Celtis occidentalis), green ash (Fraxinus pennsylvanica), and boxelder (Acer negundo), or with basswood and red oak (Quercus rubra) on lower slopes and other favorable sites. Cultivation Planting While its primary native region is the Midwest and east-central United States, the black walnut was introduced into Europe in 1629 and is also cultivated in Hawaii. It is cultivated there and in North America as a forest tree for its high-quality wood. Black walnut plantings can be made to produce timber, nuts, or both timber and nuts. Patented timber-type trees were selected and released from Purdue University in the early 1990s. These trees have been sporadically available from nurseries. Varieties include Purdue #1, which can be used for both timber and nut production, though nut quality is poor compared to varieties selected specifically as nut producers. Grafted, nut-producing trees are available from several nurseries operating in the U.S. Selections worth considering include Thomas, Neel #1, Thomas Myers, Pounds #2, Stoker, Surprise, Emma K, Sparrow, S127, and McGinnis. Several older varieties, such as Kwik Krop, are still in cultivation; while they make decent nuts, they would not be recommended for commercial planting. Pollination requirements should be considered when planting black walnuts. As is typical of many species in Juglandaceae, Juglans nigra trees tend to be monoecious, i.e..