The development of walnuts, hickory nuts, and filberts, so far as is known, is in all essentials the same as that described for the pecan nut except that the kernel or embryo begins to grow somewhat earlier in the season. However, the major portion of the filling, which consists in the thickening of the cotyledons, takes place late in the season, and only a month or a little more before the nuts mature. The period of the maturing of the nuts generally closely follows the completion of the filling of the kernels. During this period in the pecan, certain other species of hickory, the Persian walnut, chestnut, and others, food reserves are transferred from shucks, hulls, or burs to the nuts. Abscission layers are formed and shucks, hulls, or burs split open on drying out, thus partially or wholly releasing the nuts. There is a very direct relationship between the degree to which the nuts are filled and their time of and normality of maturing; well filled nuts mature early and normally, whereas poorly filled nuts mature late, if at all, and shucks, hulls, or burs fail to open properly. +Growth in Size+ The size of the nuts produced by a tree is determined by a number of factors, one or all of which may operate during the course of the season. These are: (1) Age of tree; (2) position of the nuts on the tree; (3) fertility of the soil and moisture supply, or the nutritional status of the tree; (4) size of the crop borne. In general, old trees bear smaller nuts than do younger trees. Hence size of nut for a particular variety is only relative. The first few crops produced by a tree usually consist of nuts large in size for the variety; and then, as the tree attains age, nuts become smaller in size. Young trees make longer and thicker shoot growth than do older trees. There is, then, under normal conditions, a direct relationship between the growth made by a tree and the size that the nuts attain. The more vigorous trees not only produce larger nuts than those produced by less vigorous trees, but the hulls and shells of such nuts are thicker and constitute a higher total percentage of the total weight of the fruit. The position of the nuts on a tree has an important effect on the size that they ultimately attain. In general, the nuts in the top are larger than those nearer the ground; and those on the strongest and most vigorous shoots of the top or lateral branches will attain a larger size under normal conditions than those located on weaker and shorter shoots or on the inside of the tree. Here again there is a direct relationship between growth of the tree and growth in size of nuts. All normal trees make longer and stronger shoot growth in the top than they do on the terminals of lateral branches, and the shortest and weaker shoots as well as the smallest nuts are generally on the lateral branches inside of the tree top.