The seedlings of watermelon, planted in infested soil were picked up on the first appearance of the wilt symptoms and fixed in formalin acetic alcohol. Each of them was then cut into several pieces, imbedded in paraffin. Thus the whole plant, from root to cotyledon, was dissected serially, stained in HEIDENIIAIN haematoxylin and eosin, or in safranin and gentian violet. Upon examination of these serial sections, the a u t hor attempt to draw some systematic diagrams of the affected plants, tracing the signs of the disease (Fig. I, 2, 3, 4). In these figures the longitudinal pararell linesA, B, C, etc? show the positions of the vascular bundles of each plant, the pocketlike swellings along the lines of vascular bundles show the degrees of the mycelial growth of the pathogen, and a few broken lines between the lines of vascular bundles (Fig. 2) show the presence of the mycelia outside of the bundles, mostly in the cortex parenchyma. The irregular maplike line extending to the whole figure presents the diseased area of the host tissue in which the parenchymatous elements are severely deformed. The dotted portion through out shows the necrotic area of the collenchyma tissue. Fig. 5 shows the my c elial growth along the vessels of F bundle in Fig. 1, and each figuresa, b, c, etcin Fig. 5 corresponds to each different height denoted by the signsa, b, c, etcin Fig. I. Also, in Fig. 6, each b', g', etc corresponds to the same signs without dash in Fig. 5. The relation between Fig. 3 and Fig. 8 is the same to that between Fig. i and Fig. 5. The seedling presented in Fig. i, slightly bent down at the first sign of the wilting, though in other three given by Fig. 2, 3, 4, the upper part of the stems strongly drooped at the portions presented by the dotted area in each sketch of these seedlings, drawn at the right side of each systematic figure. The seedling in Fig. 2 has been soft-rotted at the basal part of cotyledons. The mycelial. growth along each vascular bundle is curiously irregular, and several isolated colonies are formed (Fig. 1, 2, 3, 4).
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