+Second growth of the trees:+ Certain of our nut trees, such as pecan and walnuts, under some conditions have two or perhaps more periods of shoot growth during the same growing season. The first, or main period of growth, starts at the time of foliation in the spring and ends soon after the shoots flower. The second period of growth, if it occurs, may begin any time after the nuts are set, and may end any time later. This second growth seriously affects the filling of the nuts, in that food materials are consumed in producing this second growth rather than in the growth and filling of the nuts. Generally this second growth is not made until late in the season, and it usually follows a period of dry weather, when conditions again become favorable for growth. Usually this is at the time the kernels should be developing, and hence the degree of filling is affected. The seriousness of the effect on the filling of the nuts is largely proportional to the amount and duration of this second growth. A third period of growth may occur later if weather conditions are suitable. +Preceding crop:+ It has already been pointed out that nuts are storage organs and in their growth and development large amounts of food materials and minerals are removed from the tree. Under conditions of heavy crop production, the reserves of these materials left in the tree at the time of harvest are likely to be very low; and unless the trees are growing on a fertile soil and carry their leaves until frost, these reserves of minerals and elaborated food materials are not likely to be restored. Under such conditions, in the following spring the reserves are low and although there may be enough to initiate flowering and the set of nuts, they are not sufficiently high to produce well filled nuts. It is for this reason that the nuts produced in an "off crop year," even though the crop may be much lighter, may be less well filled than those produced in an "on crop year." Such nuts as pecans, hickory nuts, and walnuts transfer large amounts of potassium from the tree itself into the shucks or hulls. The kernels of such nuts are high in nitrogen, phosphorus, and magnesium as well as in oil, which is one of the most concentrated food materials and has the highest calorie value. Nitrogen reserves in the trees are readily and rather quickly replaced if adequate amounts are applied, as this element is not fixed by the soil. This is not true of phosphorus and potassium, as they are apparently taken up by the trees much more slowly than is nitrogen. Furthermore, certain soils have a high fixing power for these elements and hence they are slowly, if at all, available.