The origin and the seasonal activity of the phellogen in Acacia raddiana were investigated. The phellogen is initiated from collenchyma cells of one of the three outermost layers of the cortex. The first phellogen persists for several years. The activity is periodic and slow. The phelloderm consists of several crystal-containing cell layers, which eventually become sclerified. The activities of the phellogen and of the cambium were found not to be correlated.