In a study of maize ear rots conducted during 1933, 1935, and 1937, unsterilized natural tissues from maize ears (Reid Yellow Dent variety) in various stages of development and mature surface-sterilized whole and dissected kernels were plated on agar medium, and histological sections of kernels examined. Fusarium monili-forme [Gibberella fujikuroi: R.A.M., xx, p. 57] was found to be the most prevalent organism in maize ears. In most cases infection by this fungus and Cephalosporium acremonium[Hymenula cerealis] originated in the region of the silks, spreading thence to the kernels, pedicels, vascular cylinder, and finally the shank. Only in very few cases did G. fujikuroi infection proceed in the opposite direction, from shank to kernel. C. acre-mmium also commonly infected the lower half of the kernel surface, progressing down the ear in the region where the glumes occur; in a few cases the fungus reached the kernels by way of the butt of the cob. vaseular cylinder, and pedicels. Internal kernel infection by either fungus did not become established until the ears were approaching maturity. Infection by G. zeae [G.saubinetii] nearly always started at the tip ends of the ears, spreading downwards most rapidly in the region of the silks. Diplodia zeae and Nigrospora spp. (N. oryzae and N. sphaerica) entered the ear either at the tip or rather more frequently at the butt end, the latter type being very largely the result of local infection on the shank, D. zeae caused a more active and more extensive rot behind the advancing mycelium than any of the other fnugi A species of Moniiia, which was very prevalent in some seasons, appeared to enter the ears exclusively in the region of the silks, readily invading the pedicels and vascular cylinder and penetrating in some few cases through to the butt of cob. No internal kernel infection was found. Infections by several species of Penicillium occurred later in the season and were less prevalent than those by G. fujikuroi, but the mode of penetration was similar; internal kernel infection was, however, practically absent. Infection by G. fujikuroi and to a lesser extent by G. saubinetii, was increased by earworm (Heliothis armigera[Helicoverpa armigera]) damage to the tip of the ear: that by N. spp. and C. acremmium was only very slightly increased, and that by D. zeae did not appear to be affected by this factor. Discoloration under the husk at the butt end of otherwise healthy-looking cobs was found to be strongly indicative of infection by D. zeae, N. spp. and G.fujikuroi, while infection by C. acremonium, G. saitbinetii, and Penicillium spp. was little or not at all correlated with discoloration. Nigrospora infection was strongly related to shredded shanks. Internal kernel infection by all fungi studied was found to be most common in the tip cap, and, in a decreasing order of prevalence, in the tissues of the germ, the floury endosperm, and the horny endosperm. White streaks on the pericarp of kernels yielded G. fujikuroi, C. acremonium, and N. spp. The white colour is believed to be due to the disintegration of the cells which cease to be transparent and take on a chalky appearance.

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