to
mineral deficiencies. Among these deficiencies that have been found to
reduce tree growth and yield and to increase susceptibility to cold
injury are (1) boron, (2) copper, (3) iron, (4) magnesium, (5)
manganese, (6) nitrogen, (7) phosphorus, (8) potassium, (9) zinc, and
others. In all cases the corrective treatment to be given consists in
supplying the trees with the element or elements in which they are
deficient. These must be supplied in an available form and by such
methods that they can be absorbed by the trees.

The size of the crop of fruit or nuts borne by a tree and the length of
time between harvest and a killing freeze are important factors in
determining the cold resistance of fruit or nut trees. In test winters
many cases have been observed in which trees that matured heavy crops
during the previous summer were severely injured. Cases have been
observed in which the degree of cold injury sustained has been largely
in proportion to the size of crop matured the previous growing season.
Trees that mature the crop of fruits or nuts late in the season may be
less hardy than those that mature the crop early. It seems not only that
some material or materials are made in the leaves during late summer or
early fall which move out of them into the wood and cause it become
resistant to low temperatures, but that when a tree is maturing a crop
so much of this material goes into the fruits or nuts that if the season
is not a favorable one the wood may not attain its maximum hardiness. We
have learned that a high percentage of certain of the minerals,
carbohydrates, and oil that go to make up the kernels of the oily nuts
are transported into them during a period comprising a month to six
weeks before they are mature. In the production of a heavy crop the
amount of minerals and elaborated food materials such as proteins,
carbohydrates, and fats removed from a tree is very large. If the trees
do not carry a large healthy leaf area at the time of harvest or if
there is a killing frost at that time, the leaves have no opportunity to
elaborate more carbohydrates and other materials to replace those
removed in the crop, and as a result the trees do not develop maximum
hardiness.

To cite an outstanding example of this effect of the crop on hardiness,
I want to describe some observations I made several years ago. The late
J. B. Wight of Cairo, Ga., had a few hundred Satsuma orange trees that
bore a very heavy crop of frui