FOBEST TREES OF THE PACIFIC SLOPE. 371 



Ability to thrive in the driest and poorest soils renders it worthy of the fur- 

 ester's attention, though the cover it affords is open and scanty. 



Longevity. — Not fully determined. A tree 8J inches in diameter showed an 

 age of 49 years. 



From Western Texas (Rio Grande) through southern Net? Mexico and Arizona to south- 

 ern California. 



OCCURRED E. 



Borders of low desert mountain streams, in low canyons, on benches, and mesas ; in 

 dry, gravelly soils. Similar otherwise in occurrence, climatic, and silvical requirements 

 to mesquite. Seeding habits and reproduction undetermined. 



PARKINSONIA. 



The Parkinsonias form a small group of shrubby or low trees of little forest or 

 economic importance. They are characterized by smooth, thin bark ; the twigs 

 have one or three pronged sharp spines, or are themselves spine-like and sharp; 

 and tlii" very thin foliage is composed of clusters of long or very short two- 

 forked leaf-stems (forking close to the twig), each of which bears from five to 

 thirty pairs of very small leaflets (fig. 174). The small, showy, yellow flowers 

 (each with male or female organs) are borne in long or short, exceedingly 

 slender branched clusters (the bottom flowers opening first), and bloom from 

 spring to late summer. The fruit matured during one season is a pointed cylin- 

 drical pod (fig. 175), jointed by constrictions between the seeds and conspicu- 

 ously striped longitudinally: 1 to 8 hard, smooth, brownish seeds in each pod. 



Wood, dense, fine-grained, brown or yellowish brown, hard, and moderately 

 heavy. Small size of the trees renders the wood of little economic use. 



They are little known, but should prove worthy of attention on account of 

 their ability to thrive in hot situations, one species particularly in dry, arid 

 places. Grazing animals browse extensively upon the twigs. 



The group comprises but three species, two of which occur in southwestern 

 United States and within the Pacific region : a third species is African. 



Horse-bean ; Ratania. 

 Parkinsonia aculeata Linnaeus. 



DISTINGUISHING CHARACTERISTICS. 



The horse-bean is a short-trunked, smooth-barked tree from 15 to 2" feet 

 high and from 4 to 8 inches through, with thin, willowy, drooping or arched 



branches. The thin hark is reddish brown. Year-old twigs are greenish and 

 very minutely hairy, later becoming smooth and grayish or reddish yellow; 

 older parts of the branches hear from 1 to 3 pronged, long, keen spines at the 

 joints, from which issue 1 or 2 pairs of very long (G to 18 inches'), fiat 

 leaf-stems (each pair attached to the branch by a very short, spine-pointed 

 stem). Each stem bears from 20 to 30 pairs of extremely small, scale-like 

 leaflets (fig. 171 i. A most interesting morphological feature in the develop- 

 ment of the spines is thai when they first appear on young twigs they are the 

 short basal parts (spine-tipped) of the leaf stems, from which are given off 

 1 or 2 pairs of flat leaflet-bearing branches. These branches are later shed, 

 as the spine grows, leaving on its sides conspicuous scars. The fragrant yellow 

 flowers, three-fourths inch to 1 inch broad, and on very slender branched stems, 



