The winter of 1884 and 5 and the remarkable drouth of 1887, destroyed all of the apple orchards in Iowa, except in a few localities, where natural drainage and a very porous condition of soils, favored constant growth during the summer seasons. All of our American apples, as well as all of the apples from western Europe, have proved much too tender on ordinary prairie soils. But the Duchess of Oldenburg, Tetofsky and a few other varieties of the apple from Russia, have endured the most trying tests in all parts of the state without being harmed. As Iowa farmers are anxious to plant new orchards again, as soon as they shall be assured that their late losses will not be repeated, I will give the results of my observations and experiments in Northern Iowa since 1866; which may be of much value to many who have given but little attention to the nature and wants of different kinds of trees. If apples had not been disseminated over many degrees of latitude and longitude in Europe, Asia and America; it is probable that there would have been but few varieties, now. But they were scattered widely over the face of the earth, and as they were taken farther and farther north, they acquired new characteristics which enabled them to endure more degrees of cold. And when they were moved to places where the climate was much dryer and hotter, or moister than the one to which they were adapted, changes were effected in them after several generations, which adapted them to the unfavorable conditions which surrounded them. That I may be clearly understood, while describing the effects of unfavorable climatic conditions upon trees, I will explain the structure of trees and the principles of plant growth very briefly. All of the differents parts of trees and herbaceous plants are composed of cells. A living cell is a very small, porous and elastic sack like a bladder; which contains a semi-fluid substance called protoplasm and assimilated cell sap. After growing for a short time, each cell is divided into two parts or two new cells, each of which again divides and thus growth proceeds, forming webs of cells, which are spread one upon another during the growing season. As the webs of cells become covered w7ith webs of newer cells, their walls grow thicker; they lose their protoplasm, their ends become perforated and unite, and they are converted into tubes. Of indefinite numbers of such tubes bundles are formed, causing ducts or air passages between them. Through such ducts in the sap wood of trees, the crude sap is taken from the roots to the leaves. The pith and medulary rays are used as store rooms for reserve food materials, from which new leaves will be formed during the following spring; or they may be used to support growth when the regular supplies of assimilated sap are cut off by drouth or other causes. The wood cells of a tree which have been formed in a single season, constitute the sap-wood. The protoplasm not only constructs sap-wood during the growing season, but it forms a new inner bark, by a process similar to that which was used in the formation of sap-wood. At the same time, the old inner bark is converted into new green bark and the old green bark is changed into corky bark. The lives of cells are of very short duration. In fact, the only living cells in the limbs, body or roots of a tree, are those which contain protoplasm. Except at the tender terminal points of growth, they are formed only on the outside of the sap wood and on the inside of the inner bark, and constitute what is called the cambium layer. Therefore, all the cells of a former season’s growth are dead and worthless, for all purposes, except conducting-fluids, and supporting more elevated parts of the tree. Then it is not difficult to understand, that the seat of life is in the very thin cambium layer, between the sapwood and bark of trees; that life is really in the semi-fluid protoplasm of the billions of working cells in this layer, and that all growth takes place here. When the atmosphere becomes sufficiently warm in the spring, the protoplasm becomes active at all points between the sap wood and the inner bark of trees, and new leaves are formed from reserve food materials, which were stored up in the medulary rays and pith, near the close of the previous seasons’ growth. As soon as the leaves become sufficiently developed, a green substance called chlorophyll is formed in them by rays of light, which is always combined with particles of protoplasm.
Speer, R. P.
"Characteristics of hardy and tender fruit trees,"
Bulletin: Vol. 1
, Article 2.
Available at: https://lib.dr.iastate.edu/bulletin/vol1/iss3/2