Actively growing shoots of Vaccinium angustifolium Ait. infected with Exobasidium vaccinii (Fckl.) Woron. contain slender, septate intercellular hyphae bearing short, typically lobed haustoria. Hyphae and haustoria are also present in the apical meristem, where they often distort the shapes of the host cells they contact. The overall structure of the meristem is, however, not significantly altered and leaf primordia continue to develop from the meristem. A rather sparse hyphal system is present in young leaves, but eventually it becomes more extensive and often fills intercellular spaces in the lower portion of the leaf. Numerous haustoria are present in the leaf and are basically similar in structure to those described previously in E. camelliae var. gracilis. Haustoria contain membranous inclusion bodies, and electron-dense penetration matrices are characteristically associated with each haustorium. Overall there is very little host cell wall response to a developing haustorium and no distinct collar of host wall material is associated with the haustorium.
