378 FOREST TREES OF THE PACIFIC SLOPE. 



trend upward strongly. Gray or whitish throughout, especially the liinbs and 

 twigs, which are more or less coated with very minute white down. The trunk 

 hark of large trees is deeply and narrowly seamed, hard and rough, with small 

 scales. Very few leaves (fig. 177) are produced, and these, white-downy and 

 gland-dotted, are shed soon after reaching mature size, so that the tree or shrub 

 commonly appears leafless. Flowers deep indigo blue (hence the name " indigo 

 hush"), the outer basal covering of the blossoms (calyx) 10-ribbed, with a 

 glandular spot between each of the six upper ribs. The calyx adheres to the 

 small beaked, one-seeded pod (fig. 177), which is also gland-dotted. The shiny, 

 light brown, -kidney-shaped seeds are mottled with dark brown. 



Wood, rich chocolate brown, with a thin layer of sapwood ; moderately wide- 

 grained, soft, and rather light. Not used for any purpose. 



Longevity. — Not fully determined. A tree llf inches in diameter showed an 

 age of 40 years. 



RANGE. 



Southern California (Colorado Desert — at Agua Caliente and Toras) and eastward 

 into Arizona (to lower Gila River); south into adjacent Mexico (Sonora) and Lower 

 California (to Calamujuet). 



OCCURRENCE. 



Desert plains in dry rocky or gravelly soil. Scattered and in small groups. 

 Climatic Conditions. — Similar to those of mesquite. 

 Tolerance. — Requires full light. 



Reproduction. — Seed production rather small. Seedlings sparse and in washed mineral 

 soil. 



OINEYA. 



Olneya is a genus confined to arid parts of our southwest and containing but 

 one species which enters the Pacific region. Characters of the genus are 

 given under the following species. 



Mexican Ironwood. a 

 Olnea tesota Gray. 



DISTINGUISHING CHARACTERISTICS. 



Olnca tesota is commonly called " ironwood " in the United States on account 

 of its cross-grained, exceedingly heavy, hard wood. To avoid confusion, the 

 name " western ironwood " is proposed. " Ironwood " was applied to several 

 eastern hard-wooded trees long before this species was discovered. 



A short, thick-trunked, bushy tree from 15 to 20 feet high and from 8 to 12 

 inches in diameter ; sometimes of larger diameter. Green-gray throughout its 

 crown of thick, upright limbs and spiny twigs, and with thin, deep red-brown 

 flaky bark. Thorny twigs (fig. 17S), at first densely covered with minute, close 

 hairs, which gradually disappear with age. One or a pair of thorns, which fall 

 off in about their second year, grow from just below the leaf-stems ; the latter 

 bear from 7 to 15 white-hairy leaflets (fig. 178), in pairs, except the terminal 

 one. The leaves, partly evergreen, remain on the twigs from one spring to 

 another, falling as the succeeding foliage appears. The purplish, small flowers, 

 appearing with the new leaves, resemble pea-blossoms, and grow in short, small, 

 hairy clusters. Mature pods (fig. 178), ripe in late summer, are light russet 

 brown *and densely covered with close gland-tipped hairs ; the thick, leathery 



"Often called urbol de hierro, especially in Sonora, Mexico, where the tree was dis- 

 covered in 1852. 



