FOREST TREES OF THE PACIFIC SLOPE. 365 



California, and Mexico, is most perplexing in its characters. What may be 

 called Prosopis juliflora (Sw.) DC, inhabiting western and eastern Texas 

 and commonly a shrub with many stocky stems from a very large rootstock, or 

 sometimes a short-trunked low tree, may be distinguished fairly well by its 15 

 or 20 pairs of much-crowded, very narrow, smooth leaflets, one-third to about 

 one-half inch long, and by the smooth outer parts (calyx) of its flowers. 

 Diverging from this plant are two varieties which appear distinct in their 

 extreme forms, but which are more or less directly connected with the species 

 through intervening transitional forms. While taxonomically it is important, 

 for the sake of exactness, to trace and define these varieties, the main excuse 

 for doing so here is in the possible forest value one or both of these varieties 

 may possess. 



One variety, ProsopU juliflora velulina (Woot.) Sargent, is a tree from 30 

 to 40 feet high and from 12 to 20 inches through, inhabiting dry valleys of 

 southern Arizona and the State of Sonora, Mexico. It is the largest of our 

 species. The leaf stems, their branches, and the 12 to 24 pairs of small, narrow. 

 crowded leaflets are gray-hairy; outer parts (calyx i of the flowers minutely 

 hairy. 



The other variety, Prosopis juliflora glandulosa (Torr.) Sargent, the mesquite 

 with which this manual is directly concerned, inhabits southern California, 

 extending into Lower California and Mexico, thence eastward to eastern Texas 

 and northward into southern Kansas. This is a shrub or small short-trunked 

 tree from 15 to 20 feet high, and from G to 10 inches or more through, with a 

 rounded crown of arched or drooping branches. The leaf stems, their branches, 

 and the 6 to 60 pairs of narrow leaflets are generally smooth, the leaflets usually 

 being distant from each other (but not Infrequently crowded) and one-fourth 

 inch to nearly 2 inches long (fig. 171). Outer parts (calyx) of the flowers 

 smooth. This is the most reliable distinctive character, hut it is not invariable, 

 since these parts are sometimes minutely hairy. The fragrant yellow-green 

 flowers are produced from about May to July. Mature pods I fig. 171 i yellowish. 

 3 to 9 inches long (usually 4 to inches) by one-fourth to about one-half an 

 inch with 1 , somewhat tiat but plump: very flat and thin at first, narrowed between 

 the G to 20 seeds; pulp about seeds, which are pale brown, shiny and hard, 

 is sweet and edible. Woods of the two varieties and species are indis 

 tinguishable ; usually a deep red-brown, dense, close-grained, very hard and 

 heavy, hut somewhat brittle; exceedingly durable under all sorts of exposure; 

 sapwood very thin and lemon yellow. It has many important local economic 

 uses for building, cabinet work, and fuel in regions where it is practically the 

 only available hardwood, while the wood of the enormously developed roots 

 also supplies fuel. Only its small size and poor timber form prevent the wood 

 from being of wider commercial importance. 



For the forester mesquite is the most interesting and important tree of the 

 arid Southwest, where through the phenomenal growth of its huge deep roots 

 it defies drought conditions which kill other trees. Development of its enormous 

 roots appears to be out of -all proportion to the often insignificant stems above 

 ground, and is a subject for most profitable and interesting investigation. Ajs 

 a rule, however, the larger the stem above ground, the smaller the root develop- 

 ment; low. shrubby stems commonly have huge taproots descending to water 

 at a depth of 50 or 60 feet or more. 



A remarkable fact concerning the root wood is that it is heavier than wood 

 from the trunk. The wood of both roots and trunk contains nearly as much 

 tannin as ordinary tanbarks. A clear, yellowish gum exudes from the trunks 



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