376 FOREST TREES OF THE PACIFIC SLOPE. 



the yellow, similarly clustered flowers are closely similar to those of Parkin- 

 sonia microphylla. Cercidium is best distinguished by the flat, uncon- 

 stricted pods, which are more like bean fruits than the round, jointed pods 

 of Parkinsonia. This, together with some minor structural differences in the 

 flowers, make it desirable to maintain Cercidium as distinct from Parkinsonia. 

 Like the latter, trees of this group are desert-loving shrubs and trees. Tor this 

 reason they are of some service to the forester, since they form persistent, 

 though thin, chaparral in arid places. The moderately heavy, hard wood is 

 occasionally used locally for fuel, but not otherwise. 



One of the three species occurring in the United States (two of which are 

 small trees and the other a shrub) inhabits the southern Pacific region. 



Palo Verde; Green-bark Acacia. 

 Cercidium torreyanum (Wats.) Sargent. 



DISTINGUISHING CHARACTERISTICS. 



Green-barked acacia is a much-branched, generally leafless, short-trunked, 

 thorny tree from 15 to 25 feet high, and from 10 to 15 inches through ; some- 

 times larger. The bark of all limbs and of young trunks is smooth and light 

 yellowish green. That of large trunks is light brown with a reddish tinge ; on 

 the lower part of the trunk lightly seamed and scaly. The somewhat zig-zag, 

 smooth, green twigs (fig. 176) are thorny at the angles. The pale, minutely 

 downy leaves (fig. 176) appear in early spring, but fall very shortly after they 

 reach full size. Since the pods are shed in midsummer, the branches, as gen- 

 erally seen, are therefore bare, though a few scattered leaves occasionally re- 

 main in autumn. 



Wood, pale yellowish brown with rather thick sapwood ; heavy, but brittle 

 and cuts easily. Not known to have any economic use. 



Longevity. — No records of its age are available. Judging from the persistent 

 slow diameter growth of small stems, it appears to be long-lived. 



Southern California (Colorado Desert) and Arizona (lower Gila River Valley) and 

 gouth into Mexico (Sonora) and Lower California. 



OCCURRENCE. 



Sides of desert canyons, about sinks and depressions in arid sandhills, and on dry 

 washes ; in rocky or sandy ground. Scattered singly and in small groups. 

 Climatic Conditions. — Like those of mesquites. 

 Tolerance. — Intolerant of shade. 

 Reproduction. — Abundant seeder ; reproduction undetermined. 



DALEA. 



The genus Dalea contains a large number of shrubs and herbaceous plants 

 and but one tree species. The tree occurs in our southwest. Most of the repre- 

 sentatives belong to Mexico and South America. Foliage marked with minute 

 glandular dots (fig. 177). The small blossoms, which resemble pea flowers in 

 general appearance, combine male (pollen bearing) and female (fruit bearing) 

 organs. Fruit, a small one-seeded pod, which adheres unopened to the kidney- 

 shaped seed. Of no economic or forest importance. 



