IN 1935, Gautheret1 published an account of in vitro grafts he had obtained between fragments of cambium of Populus nigra, Salix caprea and other trees, excised and cultured on artificial media. In attempting to repeat this work, I encountered some difficulties when tissues freshly removed from the plant were employed. With cambial cultures of longer standing, however, union in vitro was obtained easily. Fig. 1 a shows two excised fragments of cambium from Vinca rosea as they appeared after two weeks culture on nutrient agar. Regeneration of callus was controlled by the natural polarity of the fragment. After these two fragments had been placed in close contact for three weeks, they were found to be firmly united (Fig. 1 b). The union was accompanied by an increased proliferation in other portions of the excised fragment.