Dr. MacDaniels: "I move that our fiscal year be from September 1st to August 31st and I move that the annual dues include a report for only the year you join."
Motion carried.
Factors Influencing the Hardiness of Woody Plants
H. L. CRANE, Principal Horticulturist[1]
There is hardly any soil or climatic condition found in the world where it is not possible for at least one or more kinds of plants to be grown. This is possible because the plants that can be grown under the most adverse conditions have special structures and adaptations with regard to periods of growth and rest or dormancy. One of the most important adaptations of nearly all trees and shrubs that shed their leaves in autumn and survive freezing weather without injury for a part of the year, is that of rest. This rest in plants is somewhat similar to sleep in animals in that it is a period in which the life process activities take place slowly. In other words, the plant physiologist defines rest in living plants as that period in which their buds will not open and grow even though the temperature, moisture, and other external environmental conditions are highly suitable for growth.
Different kinds of deciduous plants have or require rest periods of different lengths, just as some people require more sleep than do others. Two or three weeks may be enough for soft-shelled almonds but three or four months may be required for butternuts, to cite extremes. The Eastern black walnut requires more rest than most Persian walnut clones, and they more than the Southern California black walnut. Even within a species there is considerable difference in the rest period of individual seedling trees and certain clones. For example, it has been found that the varieties of Persian walnut grown in northern California and in Oregon, such as Franquette and Mayette, have the longest rest period; and those grown in Southern California, such as Placentia, Ehrhardt, Chase, and others, have the shortest rest period. It is quite possible that the clones and seedlings of the Persian walnut brought to this country a few years ago by the Rev. Paul Crath from the Carpathian Mountains of Poland may require the longest rest period of all.
The question may be asked what causes or brings on this rest period in plants and what breaks it? The scientific answers to these questions are not known at this time, but we do know some of the factors which cause the initiation of rest and how it is broken.
Tree growth is initiated in the spring with coming of warm weather and other suitable conditions. At first the rate of growth is slow; but the rate increases and goes through a maximum and then slows up again and finally ceases. On the cessation of growth in length, a terminal bud is formed and the tree begins to go into rest. This period of growth is determined by the age of the tree, the suitability of moisture and nutrient supply. Young trees grow longer during the spring and summer than do old ones. Deficiencies of soil moisture or nutrients or both cause the cessation of growth and the beginning of rest. In some trees, such as tung, cessation of growth and the initiation of rest is caused by the change from long to short day-lengths.
After rest has begun, the longer it continues the more profound or deeper it becomes until a maximum is reached, i.e., it becomes increasingly difficult, up to a certain time, to make the trees start growth again even though optimum conditions are provided. Some trees such as Persian walnuts and pecans, for example, are slow to go into deep or profound rest in late summer or fall. For this reason, there may be several cycles or periods of growth during the summer and early fall, depending on weather conditions and whether the leaves on the trees have remained in a healthy condition. Under conditions of dry weather growth stops on the Persian walnut and pecan and when this is followed by a rainy period and warm weather growth begins again. In fact in early summer a walnut or pecan tree may form terminal buds on all the shoots and remain without growth long enough for an apple or pear tree to go into complete or profound rest; then later, new shoot growth may be made from all or nearly all of the walnut or pecan shoots. Not only is this an important factor in promoting susceptibility to cold injury but in the case of bearing trees more often than not this late growth prevents the proper development of the kernels in the nuts and they are poorly filled or shriveled at harvest. Should the leaves of these trees in midsummer or later be so seriously damaged by disease or insects as to result in partial or complete defoliation, new growth is generally sure to follow even in late fall if growing conditions are suitable. This habit permits such trees to grow so late that there is much greater danger of severe injury from late fall or early winter than is the case with most other deciduous fruit trees. Furthermore, it explains why we see so much cold injury in the shoots and limbs of trees; they had grown late and had no chance to develop hardiness before killing temperatures occurred.