var. hominis H37Rv. The structure of some of these thiosemicarbazones (table I) is similar in certain respects to the structures of phenylacetic acid and some of its chlorinated oxy derivatives and their hydrazides, of salicylacetone U/ _CH:CH?CO-ChY and of dithiobiuret (NH2-CS-NH-CS-NH2), all of which possess pronounced growth regulating properties for some plants (1, 2, 3, 4). Therefore, it seemed of scientific as well as of practical interest to test the potential use in agriculture and horticulture of the thiosemicarbazones which are too toxic for practical chemotherapy of tuberculosis. The physical properties of these substances have been reported previously (?). The growth regulating properties of the thiosemicarbazone derivatives listed in table I have been tested on canes of Thompson seedless grapes (Vitis vinifera), using a technique described previously (7). Briefly, this test involves coating the apical inch of grape cuttings with a paste consisting of Carbowax 1500 in which the drug to be tested is uniformly suspended. Then the cuttings are placed in appropriate vessels with the bases immersed in water or in a solution of potassium nitrate to one and one half or two inches. In the present experiments, each grape cutting consisted of five to six internodes, each cutting received 2 to 2.5 mg. of thiosemicarbazones, and the basal ends of the cuttings were immersed in solutions of KNOs that ranged in concentration from 1 gram per liter to 0.0001 gram per liter. For each level of nitrate, the controls consisted of cuttings treated only with Carbowax 1500. All cuttings were dormant when the experiments began. Five to eight cuttings were exposed to each treatment in each experiment. Most of the thiosemicarbazones tested suppressed in some degree the normal expression of apical dominance in the budding grapevine cuttings. On the control canes the apical buds were the first, and sometimes only, ones to develop leaves. But on treated canes, the thiosemicarbazones frequently 622