The question may be asked, why is it so important that nuts be well filled? The answer is very simple, because the quality of the oily nuts is determined by how well the kernels are filled. All but one of our most important nuts--almonds, filberts, hickory nuts, pecans, and walnuts--are oily nuts; and well filled kernels contain from 50 to 75 percent or more of oil, depending upon the species. Chestnuts are starchy nuts and contain less than one percent of oil. The relationship between the degree of filling and the composition of the kernel in oily nuts is outstanding, in that the better filled nuts have a higher content of oil and a lower content of protein, carbohydrates, water, and undetermined constituents than do poorly filled nuts. Highest quality of the kernels is directly associated with highest oil content and highest degree of filling. Nut kernels that are poorly filled are often hollow, shrunken, shriveled, and chaffy. When eaten they may taste sweet, but are lacking in the oily flavor characteristic of the particular species of nut eaten. It is only in the best filled nuts that highest quality, flavor, and oil content are found. The degree to which nuts are filled or how well the kernels are developed at harvest is determined by a rather large number of interrelated factors: (1) Size of crop, or ratio of number of leaves per nut; (2) average size of nuts; (3) condition of leaves; (4) amount of second growth of the trees; (5) size of preceding crop and how well the nuts produced were filled; (6) disease and insect injury to the nuts; (7) weather conditions; (8) heterosis or effect of cross-pollination on embryo size.