Besides searching for the vector or vectors that spread the disease other important studies are in progress. Among these is the consideration of chemotherapy as a possible means of controlling oak wilt. For our purpose, plant chemotherapy may be defined as the control of disease by chemicals which are introduced into the plant. According to Dr. Paul Hoffman of the Illinois Natural History Survey, a number of chemicals have shown promise in curing small diseased oak trees when treated in a very early stage of the disease. In one instance, trees that were inoculated with the oak wilt fungus then treated with chemicals 2 years ago are still alive. The most promising results were obtained by injecting the chemicals into the soil where they are taken up by the roots and by applying chemicals directly to the foliage in a spray. Trunk injection showed least promise because of the limited distribution of the chemicals through the tree. The use of chemicals for curing wilt-infected trees is still in the early experimental stage and is not yet recommended as a practical control measure. In 1949 Wisconsin workers demonstrated the local spread of oak wilt through natural root grafts. They found that the poisoning of a single healthy tree with sodium arsenite often killed as many as 15 other trees nearby, indicating that their roots were connected. Recently the results of experiments in Wisconsin explained in part what causes the leaves of diseased trees to wilt. When a tree becomes infected it is stimulated to produce tyloses or swellings in the vessels of the wood. Therefore, the flow of water from the roots to the tree top is restricted and the leaves wilt and die. It is also known that the fungus itself produces a toxin which might be responsible for the actual killing effect on the tree. In Illinois experiments are being conducted with insects in relation to the spread of oak wilt. Insects of various species are collected from wilt-killed trees and allowed to run over or feed on laboratory cultures of the oak wilt fungus. The insects are then caged on parts of healthy trees to feed on the leaves. A single red oak treated in this way contracted the disease and died. This shows that the disease can be transmitted by an insect. Controlling the Disease