FOREST TREES OF THE PACIFIC SLOPE. 369 



ACACIA. 



Acacia is a very large group of widely distributed, world-famous trees, 

 shrubs, and herbaceous plants. Over 400 species are known in different 

 parts of the Old and New World, three-fourt lis of them in Australia. About a 

 dozen trees and shrubs occur in the southwestern United States and adjacent 

 territory. The group now contains fewer representatives Than formerly, a num- 

 ber of acacia-like members having been classed under related genera. Several 

 leguminous trees, such as the locusts (Oleditsia) and others, are popularly called 

 acacias, but technically they are not true acacias. It is exceedingly difficult to 

 find characters by which acacias may be popularly distinguished from other 

 closely related groups, which are technically separated mainly by such inconspic- 

 uous characters as the structure of their flowers. 



True acacias have astringent bark, which in some cases is very valuable for 

 tanning. When punctured, the trunk exudes a mucilaginous gum. The gum of 

 some foreign species is known in commerce as gum arabic. The true leaf is 

 compound, comprising one main stem with 2 to 3 pairs of small side branches 

 which bear several or many pairs of opposite tiny leaflets. Leaves of our 

 acacias are shed every year. Their twigs have one or two keen spines 

 (sometimes long and straight, and sometimes short and curved), commonly at 

 points where leaves or flower steins grow (fig. 173). When there are two spines 

 they form a pair. Flowers minute, often arranged in bright colored, slender, 

 single-stemmed balls, or in long, single-stemmed cylindrical clusters. An impor- 

 tant technical distinction is that the flowers, each of which usually combines 

 both male (pollen bearing) and female (fruit bearing) organs, have more than 

 50 of the bristly, usually bright yellow, thread-like organs (stamens) protrud- 

 ing from the flower body; each stamen is entirely or practically separate from 

 its fellows. Divisions of the inner (lower cup (petals) are united into a cup or 

 divided above and united at their bases I rarely, entirely separated). The fruit 

 pods, bean-like, are flat or full and rounded when mature, straight, but in our 

 species commonly twisted or crumpled, and their hard, smooth seeds usually 

 hear an oval or circular depression on each of their broad surfaces, an impor- 

 tant distinctive mark. They are all peculiarly adapted to growth, usually very 

 rapid, in poor dry soils and in hot or warm climates. As a rule, our native 

 acacias are little more than chaparral brush; they are too rarely trees to be of 

 economic importance. 



Acacias are of ancient origin, many species having existed in an early 

 geologic period. 



Only two of the dozen species indigenous in our Southwest, together with one 

 naturalized species, an- trees, and only one of these occurs within the Pacific 

 region. 



Cats Claw. 



Acacia grt ggii Gray. 



DTSTTNr.x ISIIIXc; < IIAIIACTERISTICS. 



Cats claw receives its name from the keen hooked spines on its twigs (fig. 173). 

 Very often it is only a low shrub, but usually it is a short-trunked. much- 

 branched tree from 10 to 20 feet high and from 6 to 8 inches through: occasion- 

 ally it is somewhat taller and thicker. The angled twigs are minutely hairy and 



"Some exotic acacias produce simple, leaf -like msans i phyllodia i which are morpho- 

 logically only leaf stems dilated into the form of a simple leaf blade. 



