The cucumber, Cucumis sativus, is an ancient cultivated vine of South Asian origin, grown across the old world for its cool, watery fruit. It earns a memorable place in the Hebrew Bible: in the Book of Numbers the Israelites in the desert weep for the food of Egypt, the cucumbers and melons, the leeks, onions and garlic they ate freely there, against the monotony of manna, one of scripture's sharpest images of the appetite that looks back to bondage. The English phrase cool as a cucumber records the plain fact that the fruit's interior stays cooler than the surrounding air.
The cucumber's later Roman history supplies a vivid anecdote: Pliny the Elder records that the emperor Tiberius was so fond of cucumbers that he had them grown for him every day of the year, forcing the vines under frames glazed with sheets of translucent mica, specularia, a primitive greenhouse built to defeat the seasons for a single ruler's appetite. The plant reached the Mediterranean from South Asia by way of Egypt well before Roman times, and its extremely high water content, some ninety-six per cent by weight, is the simple physical fact underlying both its reputation as a cooling food and the English idiom drawn from it. It has remained ever since one of the most widely cultivated vegetables on earth, eaten fresh, pickled and preserved across nearly every culture it has reached.