Smooth-barked loosely-branched deciduous trees. Twigs very thick, somewhat 3-sided, with prominent lenticels; pith large, roundish. Buds solitary, sessile, relatively small; terminal bud lacking. Leaf-scars alternate, shield-shaped, large; bundle-traces 9 or more; stipule-scars none.

Fig. 175. Ailanthus altissima.

1. A. altissima (Mill.) Swingle .Tree of Heaven. (A. glan-dulosa Desf.). A tree to 20 m. high, having relatively smooth bark with pale stripes; twigs puberulent. Introduced from Asia, widely naturalized from cultivation, often weed-like and competing with native trees (Fig. 175).