XI. ULMACEÆ.
Trees, with watery juice, scaly buds, terete branchlets prolonged by an upper lateral bud, and alternate simple serrate pinnately veined deciduous stalked 2-ranked leaves unequal and often oblique at base, conduplicate in the bud, their stipules usually fugaceous. Flowers perfect or monœciously polygamous, clustered, or the pistillate sometimes solitary; calyx 4—9-parted or lobed; stamens 4—6; filaments straight; anthers introrse, 2-celled, opening longitudinally; ovary usually 1-celled; ovule solitary, suspended from the apex of the cell, anatropous or amphitropous; styles 2. Fruit a samara, nut, or drupe; albumen little or none; embryo straight or curved; cotyledons usually flat or conduplicate. Five of the thirteen genera of the Elm family occur in North America. Of these four are represented by trees.
CONSPECTUS OF THE NORTH AMERICAN ARBORESCENT GENERA.
Fruit a dry samara, or nut-like. Flowers perfect; fruit a samara.1. [Ulmus.] Flowers polygamo-monœcious; fruit nut-like, tuberculate.2. [Planera.] Fruit drupaceous. Pistillate flowers usually solitary.3. [Celtis.] Pistillate flowers in dichotomous cymes.4. [Trema.]