Perhaps you thought that the great ages of discovery and exploration, circa 1492 and all that, were based on quests for silk and spices, porcelain and gold. True--but the quest was for rhubarb as well. That thesis is convincingly demonstrated in this prodigious work of scholarship by Univ. of Maryland historian Foust. Why rhubarb? And what rhubarb? Well, the ancients knew of the wonderful cathartic powers of the roots of this robust plant rumored to be native to somewhere beyond Greece and Rome (""rhu"" was also ""rha,"" supposedly an old name for the Volga river; ""barb"" meant somewhere beyond the civilized realms of the Mediterranean). It appears that the pulverized roots and rhizomes of rhubarb provided both gentle purgative powers as well as ""binding"" or astringent qualities. But what rhubarb? The true or ""officinal"" medicinal rhubarb is not to be confused with the red-stalked plant served up as stewed fruit or pie, nor with various rhubarbs of inferior medical potency. The very best came from China, introduced into the West through Russian caravans traveling overland in the north or by Arabian trade routes or coastal merchants in the south. Not until the opening of China in the last century was the source officially established. Foust's impeccable account is a feast for scholars, but perhaps too rich for some casual readers. Nevertheless, the text, with its detailed cultural lore, botany, history of medicine, pharmacology, trade and exploration, plus a cast of hundreds, makes an essential point: It was the long domination of the humoral theory of disease that created the market for rhubarb. The need to expel four humors from the body to cure disease drove the quest for the kinder, gentler, ""perfect"" purgative. And it works, too.