Altho crown gall is one of the most serious diseases of apple trees in the nursery, effective control measures for root-grafted stock have not yet been found. This is doubtless due to previous lack of definite knowledge of the causal agent. Now, due to the excellent work of Erwin F. Smith and C. D. Townsend, Bacteriurn turnefaciens, Sm. and Tw., has been shown to cause this disease. Later, Smith, Brown and Townsend contributed many other important facts pertaining to the pathogenicity and biology of the organism. As a result of these studies, experiments on control measures have been made possible and their successful conclusion has been made probable.