POPULUSWesmael (IS) groups the species of poplars in three tribes which are separated chiefly on the basis of presence or absence of gluten covering the terminal buds, number of stamens, and shape of petioles. Five species were studied, representing the three tribes; P. alba, P. grandidentata, and P. tremuloides the first, P. deltoides the second, and P. candicans the third. TEXT FIG. 10. Populus tremuloides '(. Diagrams showing origin, course, and distribution of the vascular supply to the pistillate flower of a typical poplar. a, section in median posterior-anterior plane; b, bract; ped, pedicel; p, pistil, dis, disk. b to g, transverse sections of flower at successively higher levels, A-A, B-B, Ce-C, etc.; [s, floral strand; bb, bract bundle; ped, pedicel; pb, vascular supply to pistil; dis, disk; disb, vascular supply to disk; 0, ovary; mcb, and cp, median carpellary and placental bundles.