SUMMARYWall ontogeny during sporidial budding inSorosporium consanguineumwas studied. Primary buds developed through expansion of all layers of the mother-cell wall. Subsequent buds arose through expansion of wall material which originated beneath, and protruded through, the outer layers of the mother-cell wall. This material was interpreted as the mother-cell septum formed during the previous budding process. Successive budding resulted in the formation of annellations at the apex of the mother cell. Septation was initiated by centripetal invagination of the plasmalemma at the junction of the mother and bud cells in which a double septum was formed prior to abscission. Our observations are compared with those reported for other yeastlike fungi and yeasts.