THE chemotropism of pollen tubes and of fungus hyphae and the chemotaxis of various unicellular organisms have received considerable attention in the great mass of work which has been done on the sensitive activities of plants. There is probably a well-defined notion that terrestrial roots, which are known to be hydrotropic, are also chemotropic. The unequal distribution of minerals in the soil, and of decaying organic matter, can be thought of as furnishing opportunity for the development of chemical response as a biological adaptation. In literature there seems to be no record of work done to test the ability of roots to respond to a chemical stimulus by changing their direction of growth. This test has now been made, and the results are recorded in the following pages.