4 BULLETTX 933, TJ. S. DEPABTMENT OF AGRICULTURE. 
INFLUENCE OF SOIL AND CLIMATE UPON DISTRIBUTION. 
Throughout its wide range the local distribution of walnut is con- 
trolled by climatic and soil factors, which affect not only its abun- 
dance and commercial value but also the other species with which 
it characteristically associates in the forest. In general, walnut is 
found on rich, moist but well-drained soils. It is more dependent 
upon these conditions than are many of its associates, and a rela- 
tively slight inferiority in any of these respects may be reflected 
either in a scarcity of walnut or in slow and scrubby growth. Its 
dependence upon good soil is more marked, however, in regions in 
the western part of its range, which have a relatively scant precipi- 
tation, than it is in well-watered regions like those in the southern 
Appalachians. In the latter situations it makes a better develop- 
ment on rocky and shallow, though by no means sterile, soils than 
could be expected elsewhere, compensation for the deficiency in soil 
qualities being made by the abundance of the summer rains. 
TTest of the TTabash River and in the Mississippi Valley below 
Illinois walnut of good development is almost invariably on rich 
bottom lands. An exception to this is its occurrence in the Boston 
Mountains of Arkansas, where because of the heavier precipitation 
it is found on flat mountain tops and benches. It is. however, by no 
means a stream-bank tree in the sense in which sycamore, river birch, 
and willow are. These species, though frequently growing near by, 
are rarely seen in intimate mixture with walnut except in the moister 
places in the eastern part of its range. This is probably because the 
soil for walnut must be not only moist but well drained and aerated 
as well — a fact which, no doubt, also explains in large measure the 
lack of walnut in such places as the Mississippi bottom lands, which 
are subject to jDrotracted flooding. The deficiency in soil aeration 
may also be responsible for the exceedingly slow growth and virtual 
failure of certain plantations on rich but exceedingly compact bot- 
tom-land soils, heavily sodded and never thoroughly broken. 
LOCAL FORMS OF GROWTH AND ASSOCIATED SPECIES. 
Walnut is found in three characteristic situations — as scattered 
field and fence-corner trees, as scattered trees in hardwood stands, 
or as pure stands, usually on the edge of the hardwood forest. 
In fields, particularly in the Ohio River basin, it sometimes rep- 
resents a remnant. of the original stand, left because of its value when 
the land was cleared for agriculture. The fence-corner trees have 
come up because the uncultivate.d soil attracted squirrels to bury the 
nuts there and because in such situations the trees were protected 
from injury. Ever since the days of the great popularity of walnut 
furniture there has been a tendencv amon^r farmers to conserve this 
