From Much Depends On Dinner : The Extraordinary History And Mythology, Allure And Obsessions, Perils And Taboos, Of An Ordinary Meal by Margaret Visser:

At the end of the seventeenth century, John Evelyn wrote a book on salads, called Aceteria (things in vinegared dressing): A Discourse of Sallets, in which he extols the reign of lettuce over the salad bowl. “And certainly ‘tis not for nothing,” he wrote, “that our Garden-Lovers, and Brothers of the Sallet, have been so exceedingly Industrious to cultivate this Noble Plant, and multiply its Species; for… by reason of its soporiferous quality, lettuce ever was, and still continues the principal foundation of the universal tribe of Sallets, which is to cool and refresh, besides its other properties,” which include inducements to “morals, temperance, and chastity.”