390 TREES OF NORTH AMERICA 



4. SORBUSL. Mountain Ash. 



Trees or shrubs, with smooth aromatic bark, stout terete branchlets, large buds covered 

 by imbricated scales, the inner accrescent and marking the base of the branchlet by 

 conspicuous ring-like scars, and fibrous roots. Leaves alternate, pinnate in the Ameri- 

 can species, the pinnae con duplicate in the bud, serrate, deciduous; stipules free from the 

 petioles, foliaceous. Flowers in broad terminal leafy cymes; calyx-tube urn-shaped, 5-lobed, 

 the lobes imbricated in the bud, persistent; petals rounded, abruptly narrowed below, white; 

 stamens usually 20 in 3 series, those of the outer series opposite the petals; carpels 2-5, 

 usually 3; styles usually 3, distinct; ovules 2 in each cell, ascending; raphe dorsal; micropyle 

 inferior. Fruit a small subglobose red or orange-red pome with acid flesh, and papery 

 carpels free at the apex. Seeds 2, or by abortion 1, in each cell, ovoid, acute, erect; seed- 

 coat cartilaginous, chestnut-brown and lustrous; embryo erect; cotyledons plano-convex, 

 flat; radicle short, inferior. 



Sorbus is widely distributed through the northern and elevated regions of the northern 

 hemisphere with three or four species in North America of which one is arborescent, and 

 with many species in eastern Asia and in Europe. Of the exotic species, Sorbus Aucu- 

 paria L., the common European Mountain Ash, or Rowan-tree, with several of its 

 varieties and hybrids, is often cultivated as an ornamental tree in Canada and the 

 northern states and has become sparingly naturalized northward. 



Sorbus is the classical name of the Pear or of the Service-tree. 



1 . Sorbus americana Marsh. 



Leaves 6'-8' long, with 13-17 lanceolate acute taper-pointed leaflets unequally cuneate 

 or rounded and entire at base, sharply serrate above with acute often glandular teeth, 

 sessile or short-stalked, or the terminal leaflet on a stalk sometimes \' long, when .they un- 



Fig. 347 



fold slightly pubescent below, at maturity membranaceous, glabrous, dark yellow-green, 

 on the upper surface, and paler or glaucescent and rarely pubescent on the lower surface, 

 2'-4^' long, i-1' wide, with a prominent midrib and thin veins; turning bright clear 

 yellow before falling in the autumn; petioles grooved, dark green or red, 2'-3' in length, the 

 rachis often furnished with tufts of dark hairs at the base of the petiolules; stipules 

 broad, nearly triangular, variously toothed, caducous. Flowers appearing after the leaves 

 are fully grown, f ' in diameter, on short stout pedicels, in flat cymes 3'-4' across, with acute 

 minute caducous bracts and bractlets; calyx broadly obconic and puberulous, with short, 



