362 FOREST TREES OF THE PACIFIC SLOPE. 



iu only one genus of our trees). These consist of a prominent central stem 

 which either directly gives off a number of pairs of rounded or pointed leaves 

 (leaflets) along its two opposite sides or gives off branches and subbranches 

 which in turn bear their leaves in this way. The central stem corresponds 

 morphologically with the midveins of simple leaves, such as those of maples and 

 oaks, and when shed in autumn parts from the twigs just as in these latter 

 trees. Leguminous trees are further and most distinctly characterized by their 

 beans, or bean-like fruit pods, all matured in one season, some of which resem- 

 ble ordinary garden peas and beans and some of which have jointed or twisted 

 pods in which each seed is separated from its fellows by intervening constric- 

 tions; while in some members the fruit is structurally a bean-pod, but unlike 

 ordinary ones in containing but a single seed, this, however, bean-like in shape. 

 Flowers of many members of this family are pea-like or bean-like and combine 

 male (pollen bearing) and female (seed bearing) organs, or the organs of one 

 sex are suppressed and the flowers are male or female only. They are borne 

 on different parts of the same tree or branch or on different trees. In one sec- 

 tion of Leguininosse the flowers (bisexual in each blossom) bear no resem- 

 blance to pea or bean flowers, but appear like bristling, stiff, yellow, white, red, 

 or pink threads, arranged in ball-like or cylindrical bodies. 



PROSOPIS. MESQUITES. 



The mesquites form a group of small or medium-sized trees and shrubs, all 

 of which inhabit subtropical or tropical countries, with few representatives in 

 the United States. Their wood is heavy, very hard, strong, durable, and of 

 considerable local economic use ; but on account of the small size and poor tim- 

 ber form of the trees it is of only secondary and limited commercial importance. 



They are characterized usually by their 2-forked, sometimes 4-forked leaf 

 stems, with from 5 to 20 or more pairs of small leaflets and often a pair of 

 slender keen spines at the base of the bud from which the leaf stems grow. 

 At the base of the main leaf stem and of its forks minute glands (dots) are 

 usually found. The leaves are shed every autumn. Flowers (bisexual), minute 

 and densely arranged in long cylindrical clusters (in our species), with 

 slender stems from buds on twigs of the previous year's growth. Fruit, a long 

 slender, and flat bean-like pod (fig. 171), or a cylindrical, spirally marked pod 

 (fig. 170), neither of which opens of its own accord to liberate its smooth, small 

 hard beans, each of which lies in a separate cell of the pod. The seeds depend 

 for their distribution upon flood-waters and upon cattle and other animals which 

 feed upon them and thus assist in disseminating and sometimes in planting 

 them. Seeds do not, however, germinate except when covered by or placed in 

 contact with continuously moist soil. The ripe, dried pods, made into coarse 

 flour, have long been used for food by southwestern Indians and Mexicans. 

 Two species and two well-marked varieties occur in southwestern United States 

 and adjacent territory on the south. 



Screwpod Mesquite. 



Prosopis odorata ° Torrey and Fremont. 



DISTINGUISHING CHARACTERISTICS. 



Sometimes a short-trunked tree from 15 to 20 feet high, and from 3 to 8 (rarely 

 10 to 12) inches in diameter, but usually shrubby, with numerous stems; bark 

 of large trunks pale reddish brown, shaggy with loose strips. Year-old twigs 



o The technical name maintained hy other writers is Prosopis pubcscens Bentham 

 (1846) ; Prosopis odorata T. and F. was published in 1845 and is clearly entitled to 

 recognition on the ground of being the first name applied to this tree, except for the 



