The development of infection of the ovary of Newal barley (Hordeum vulgare L.) by the ergot fungus, Claviceps purpurea (Fr.) Tul., was traced from the time of inoculation until formation of the sclerotia. Penetration took place within 24 hours near the base of the ovule. Initially, colonization was intercellular and confined to the ovary wall but by the fourth or fifth day the fungus began to move intracellularly, penetrating the ovule and also growing out onto the surface of the ovary to form a hymenium. Spores and honeydew were produced within five days of inoculation. The advancing hyphae were seldom found in stylar or stigmatic tissue and then only after the parasite was well established. Usually these structures are pushed upward to form a cap on the maturing sclerotium.