The present paper reviews certain of the essential features which characterize the growth of crown gall, especially as they bear upon the general problems of cancer. In addition, it contains a number of new observations, which appear to bring this vegetable growth into relation with the group of tumors described as embryomata. II. CROWN GALL In brief, crown gall as here described is a plant disease, tumorlike in nature, which is produced by a bacterial organism. It is a growth very common in many parts of the world (North America, South America, Europe, Asia, Africa) on a great variety of cultivated plants, and on some wild ones. It is known by many names, but generally in the United States as “crown gall,” because it occurs very often on what the gardeners call the crown of the plant, i.e., on that part where stem and root join, but it may occur on any part of the plant (Pl. I, figs. 1 and 2). III. NATURE OF THE TUMOR Arguments against the cancerous nature of plant tumors based upon conditions in those tumors of turnips and cabbage which have been most studied by animal pathologists, or in over-growths due to gall-insects, or to various fungi, or even to other bacteria, do not apply to this tumor. Crown gall, is not an hypertrophy due to the enormous enlargement of a few special parasitized cells, like the bacterial root nodules of legumes or the finger-and-toes of cruciferous plants, ascribed to the slime-mold Plasmodiophora brassicae, nor is it a granulomatous hyperplasia in which the bacteria are located in cavities or pockets between the cells and pass by way of the vascular system into distant regions, like the olive tubercle, due to Bacterium savastanoi. On the contrary it is a peculiar hyperplasia, the bacteria which are the cause of it developing sparingly and only within the cells, which they compel to divide early and repeatedly, so that a great mass of non-capsulated, small-celled tumor tissue arises (Pl. I, figs. 3 and 4, Pl. II, figs. 5 and 6, and Pl. IV, figs. 17a, 18) in which the bacteria themselves are invisible. These numerous, small, incompletely developed, atypical, unripe cells are endowed with enormous reproductive capacity which is not under the physiological control of the plant (Pl. III, figs. 7 to 13 and Pl. IV, figs. 14 to 16—sunflower), and the continued development of which is detrimental to the plant both locally and constitutionally. Various grades of anaplasia exist, some of the cells in the tumor reaching nearly the normal size and form before division, while others divide quickly again and again, remaining quite embryonic. The tumors, even when deep-seated, are incompletely vascularized (Pl. IV, figs. 17, 18, and Pl. VIII, fig. 26), often quite fleshy, and very subject to decay (Pl. V, fig. 20). These conditions naturally result in the production of open wounds, which are subject to a variety of secondary infections, some of them very harmful to the plant. The tumor when inoculated on fleshy roots such as the sugar beet is often larger than the root itself.