Another possibility is that the original Lamb Walnut was a chimera. Such a tree would have mixed tissues in its growing points, some having the curly grain character and others not. In such a tree some scions would produce curliness and others straight grain. It may be that these were mixed in the original collection. A third possibility is that curliness is produced by the interaction of several factors, one a tendency to curliness inherent in the Lamb tree and the others environmental such as growth rate, nutrient supply, the nature of the soil or other such conditions. Theoretically curly grain in walnut or any other tree is related to the nature of the growth of the cambium layer. In normal growth the cells of this layer are much elongated as seen in tangential section and are relatively straight. The nature of these cambium cells is shown in figure 2. [Illustration: Fig. 2. The cambium of a straight-grained black walnut tree as seen in tangential section. The nature and regularity of these cells determines the nature and regularity of the cells of adjacent wood and bark (x 150).] It is well known from studies of cambial growth that irregularities 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).]