Egyptians collected the sap of gum arabic to use as an adhesive.
The catclaw tree (Acacia greggii) of the American Southwest gets its name from the talon-like thorns covering its branches. Likewise, the catclaw's cousin, gum arabic (Acacia senegal), has sharp thorns. But, it's the sap, not the thorns or wood, that's made the reputation of this native of northwest Africa and the Middle East.
A short tree, growing to only 20', gum arabic has reddish brown wood that local craftsmen convert into novelties, such as turnings and jewelry. Its water-soluble sap, though, eventually travels the world.
During droughts, the deeply fissured gray bark of the tree splits, exuding a resinous sap that slowly forms into 2" long tears. Ancient Egyptians collected these tears and used the gum as an adhesive to hold gems and glass in jewelry and pottery, and as a paint base. To Arab healers, however, the sap cured coughs and sore throats.
Known today a gum arabic, it plays many commercial roles. In the pharmaceutical industry, for example, it binds the ingredients in pills and tablets. Bakers add gum arabic to their batter to build body and gain texture. It's also used in polishes, watercolors, and other paints. Yet, it's as the mild (and slightly unpleasant tasting) adhesive on the backs of stamps and envelope flaps that most people contact gum arabic. With a lick and a promise, it seals a letter and tickets it for travel.
Illustration: Jim Stevenson