Morphogenesis in caulinar fragments of Aucuba japonica Thunb. in vitro. — Caulinar fragments ofAucuba japonicaThunb. are grownin vitroin different media. They show an obvious polarity; in fact only the basal section surface shows a vigorous proliferation and is able to form roots. When this surface emerges it gives rise to a green luxuriant callus; when the same surface is immersed it forms a protuberance in the shape of crateriform invaginations. Our histological studies indicate not only the connection between new proliferations and the pre-existent vascular tissues, but also the areas where the pseudothalli originate. The changes in the cortex and the central cylinder which are caused by thein vitrocultures were observed.