1. The floral anatomy of Ailanthus excelsa, A. malabarica, A. grandis, A. glandulosa, Picrasma quassioides, and Brucea sumairana, members of the tribe Eusimaroubae of the Simaroubaceae, is described. 2. The actinomorphic dichlamydeous flowers are either pentamerous or tetramerous in all the cycles. They are unisexual, except in Brucea, and are considered to have been derived from bisexual flowers. 3. The aestivation of the perianth is either valvate or imbricate. Each perianth lobe receives a single vascular trace which divides into three to five in higher regions. 4. The androecium may be haplostemonous, diplostemonous, or obdiplostemonous. The obdiplostemony of Ailanthus is considered to have resulted from the adnation of the traces to petals and antipetalous stamens. Although the haplostemonous condition of Picrasma and of the female flowers of Ailanthus is considered to have been derived from an obdiplostemonous state by suppression of the outer whorl, that of Brucea is regarded as derived from a dipl...