Infected seed of the susceptible wheat varieties Hybrid 46 and Vilmorin 27 was obtained by artificial inoculation. In an infected embryo, loose smut mycelium is present in the scutellum and growing point region. When germination of the seed commences, the fungus also becomes active and the mycelium is carried upwards by the elongation of the epicotyl. This elongation carries the node of the first foliage leaf to a position near the ground level. This node, which contains mycelium, becomes the first crown node. Development then takes place in the crown, until by about April the entire adult plant is laid down in the crown region. The nodes, internodes, and ears of each tiller can be recognized within the leaf sheaths, but their combined length is only about 1/4 in. Loose smut mycelium permeates the whole structure. Expansion of the stems begins from below upwards, the lowest internode of each tiller being the first to elongate. The mycelium already present in the ear is carried up with it, and on emergence the ear is completely replaced by spores. Variations in the amount and forms of infection are discussed. Field observations and a time-of-sowing experiment have shown that loose smut infection is not influenced by environmental conditions after sowing.