arities in
the growth of the cambium are reflected in the irregularities in the
shape and position of the wood fibers and vessels, which it forms.
Ordinarily, if the cambium is wounded, the first cells formed are
irregular in shape and orientation but after a wound is healed over the
cambium cells resume their normal position. In parts of trees in which
the grain is irregular or confused such as in the inner angle of
crotches the shape of the cambium cells determines the nature of the
grain beneath as shown in figure 3 (Ref. 1). This has been established
also in the study of the nature of spiral-grained Douglas Fir and in
various experimental work where it has been possible to change the
direction or extent of the cambium cells through various experimental
means. (Ref. 2)

[Illustration: Fig. 3. Section through cambium and underlying wood in a
crotch of an apple tree where the grain of the wood is not straight. The
shape and direction of the wood fibers or grain of the wood, and bark is
determined by the shape and direction of the cambium cells that form
them (X 100).]

There seems to be no doubt, therefore, that curly grain in walnut is
directly related to the curly condition to be found in the cambium,
which produces such curly grain. The basic question to be resolved is
what makes the cambium of a curly-grain tree assume the curly or wavy
character. As indicated above, one hypothesis is that several factors
may be operating. For example, a tree might have the inherent capacity
to produce wavy grain but would only do so under special environmental
conditions. These environmental conditions might be related to rapidity
of growth, water and nutrient supply, or various other habitat
characteristics, which affect the nature of growth. The fact that the
tree in question at Ithaca was growing rapidly might have been
responsible for the failure of the curly grain to develop. There is
evidence that trees with figured grain grow slowly. (Ref. 3, 4) On the
other hand the specimens from the tree at Beltsville, Maryland, were
from a slowly growing plant and did not show curly grain.

Another hypothesis is that development of the curly grain is dependent
upon the foliage of the tree. This has been demonstrated to be true in
instances where the foliage of fruit plants determines the
characteristics of the growth of the trunk and roots and of the fruit
itself. (Ref. 5, 6) It might be, therefore, that the failure of this
particul