26 HOUGH'S AMERICAN WOODS. 



A small tree, occasionally attaining the height of 30 ft. (10 m.), and 

 16 or 18 in. (0.50 m.) in diameter of trunk, with irregular top of many- 

 fine tough branchlets, these and even the large branches covered with a 

 thin, smooth, yellowish green (pea green) bark. The bark of trunk 

 finally becomes fissured longitudinally and the smooth green epidermis 

 persists for a time on the summits of the ridges thus formed. Finally that 

 scales off and leaves a light brownish-gray bark, rough with irregular 

 longitudinal thick-scaly ridges. 



It is a tree of handsome, curious aspect, owing to the generally pre- 

 vailing light green color throughout its top, its numerous fine branches 

 and very limited foliage, and even that only seen for but a few weeks of 

 the year. It affords a delightful relief against the everywhere prevailing 

 sand-color of the dreary parched desert in which it grows. 



HABITAT. The " washes " and depressions among the sand-hills of 

 the Colorado Desert in southern California, and the region of the Gila 

 River in Arizona. 



PHYSICAL PROPERTIES. Wood heavy, moderately strong and soft, com- 

 pact, occasionally figured and susceptible of a smooth satiny polish. 

 The heart-wood is small and of a strong and very disagreeable odor when 

 fresh ; the abundant sap-wood is of a rich clear light-yellow color and of 

 rather pleasant odor. Specific Gravity, 0.6531; Percentage of Ash, 1.12 ; 

 Relative Approximate Fuel Value, 0.6458; Coefficient of Elasticity \ 

 55839 ; Modulus of Rupture, 546 ; Resistance to Longitudinal Pressure, 

 417 ; Resistance to Indentation, 226 ; Weight of a Cubic Foot in Pounds^ 

 40.70. 



GENUS PROSOPIS, LINN^US. 



Leaves bi pinnate with one or two (sometimes more) pairs of pinnae, each with 

 several small, entire, rather rigid leaflets; stipules none and petioles, etc., usually 

 furnished with minute glands, Flowers regular, small, greenish, and usually sessile 

 in cyllindrical or globose, axillary, pedunculate spikes or heads ; calyx campanulate, 

 with 5 very short teeth valvate in aestivation ; petals 5, connate at first below, at 

 length free, distinct, tomentose within (in our species), hypogynous, valvate in aesti- 

 vation; stamens 10, free, exserted, those opposite the calyx-lobes rather the longer, 

 with oblong, versatile, introse, 2-celled anthers, dehiscent by lateral longitudinal 

 slits, and connective usually tipped with a minute deciduous gland ; pistil with fili- 

 form style, minute stigma and villose (in the American species) ovary containing 

 many anatropous, suspended ovules in 2 ranks, from the inner angle of the ovary. 

 Fruit a linear coriaceous legume, compressed or nearly terete, straight, falcate or 

 twisted into a spiral, indehiscent, with usually thick spongy mesocarpand partitions 

 between the numerous compressed ovate oblong seeds, which have a crustaceoua 

 testa and contain horny albumen, an embryo with short straight radicle and flat 

 cotyledons. 



Genus represented in the United States by small trees and shrubs in the arid 

 regions of the Southwest. (The name Prosopis is the ancient Greek name of the 

 Burdock and is of obscure application here.) 



