ROOT GRAFTING IN TREES

Abstract

Rigg and Harrar (1931) in a study of root systems growing in sphagnum report that excessive root fusion often occurs in sphagnlum peat. They attribute the fusion to the swaying of the trees, which wears away the bark on the roots so that the meristematic areas of different roots are brought into contact. They state also that fusions of the stemis of Alnuts ore gana which have been rubbed together by swaying in the wind are commonl in the Seattle region. Small (1932) has described natural grafts in stems of four species of trees. He believes that rubbing together of the stems, or branches, is the cause of the fusiolns. Millner (1932) has studied stem grafting in Hedera. helix and has shown that attrition of the bark by rubbing of stems, or by other means, is unnecessary in the process. Examples of stem grafting in forest trees are known to most botanists and are generally thought to be due to wearing away of the bark at the points of contact by the waving of the branches in the wind. However, the writer has seen grafts in tree stems which could not be explained in this way, and in tropical countries he has observed, in various species of strangling figs, thousands of grafts where the bark had not been disturbed in any way by external m-iealns. The strangling figs represent the most remarkable series of natural grafts to be seen anywhere, and it appears that the lightest contact between two branches or two roots is sufficient to cause their union. From these observations the author has been led to question whether any removal of bark by friction is needed to bring about grafting in tree roots. Comiparatively little is knownl about the root systems of our forest trees, and it is a matter of regret that earlier botanists did not undertake a study of tree roots at a time when great areas in the United States were being denuded of their forests. So little land is being cleared at the present time that one seldom has an opportunity to observe many root systems of any one species. The cost of grubbing out mature trees for the purpose of making studies on their roots is, of course, prohibitive. Occasionally, opportunities to make root studies on one or two species are offered by circumstances, and it is to be hoped that botanists will take advantage of them before they become even fewer. The present paper represents the utilization of such opportunities.