622 TREES OF NORTH AMERICA 



ular punctate. Fruit ovoid, pubescent, glandular, twice as long as the calyx, tipped with 

 the remnants of the recurved style; seed }' long, pale brown irregularly marked with dark 

 spots. 



A tree, 18-20 high, with a short stout contorted trunk sometimes 20' in diameter and 

 divided near the ground into several upright branches, and branchlets reduced to slender 

 sharp spines coated with fine pubescence, bearing minute nearly triangular scarious cadu- 

 cous bracts, marked by occasional glandular fistules, and developed from stouter branches 

 hoary-pubescent when young, becoming glabrous in their third year and covered with 



Fig. 568 



pale brown bark roughened with lenticels and as it exfoliates showing the pale green inner 

 bark; more often a low rigid intricately branched shrub. Bark of the trunk dark gray- 

 brown, nearly %' thick, deeply furrowed, and roughened on the surface by small persistent 

 scales. Wood light, soft, rather close-grained, walnut-brown in color, with nearly white 

 sap wood of 12-15 layers of annual growth: 



Distribution. Valley of the lower Gila River, Arizona, through the Colorado Desert 

 to San Felipe and Palm Springs, Riverside County, California, and southward into Sonora 

 and Lower California. 



15. ROBIN1A L. Locust. 



Trees or shrubs, with slender terete or slightly many-angled zigzag branchlets, without a 

 terminal bud, minute naked subpetiolar depressed-globose axillary buds 3 or 4 together, 

 superposed, protected collectively in a depression by a scale-like covering lined on the inner 

 surface with a thick coat of tomentum and opening in early spring, its divisions persistent 

 during the season on the base of the branchlet developed usually from the upper bud. 

 Leaves unequally pinnate, petiolate, deciduous; leaflets entire, penniveined, stipellate, 

 reticulate- venulose, petiolulate; stipules setaceous, becoming spinescent at maturity, per- 

 sistent. Flowers on long pedicels, in short pendulous racemes from the axils of leaves of 

 the year, with small acuminate caducous bracts and bractlets; calyx campanulate, 5- 

 toothed or cut, the upper lobes shorter than the others, cohering for part of their length ; 

 corolla papilionaceous, petals shortly unguiculate, inserted on a tubular disk glandular 

 on the inner surface and connate with the base of the calyx-tube; standard large, reflexed, 

 barely longer than the w 7 ing- and keel-petals, naked on the inner surface, obcordate, re- 

 flexed; wings oblong-falcate, free; keel-petals incurved, obtuse, united below; stamens 

 10, inserted with the petals, the 9 inferior united into a tube often enlarged at base and 

 cleft on the upper side, the superior stamen free at the base and connate in the middle 





