Universal Boon to the Salad Bowl
Lettuce (Lactuca sativa) is without doubt the world's most popular salad plant. Both its common and its Latin name are based on an easily noticeable characteristic-it has a heavy, milky juice. The word "lettuce" is probably derived from the Old French laitues (plural of laitue), meaning "milky," referring to this plant. The Latin root word lac ("milk") appears in the Latin name lactuca.
The ancient Greeks called lettuce tridax; the old Persians, kahn. Although its culture was widespread in ancient times, it is neither so old nor was it so widely grown in prehistoric times as a number of other garden crops.
Lettuce Often Found Wild
Cultivated lettuce is closely related to the wild lettuce, L. scariola, from which it was doubtless derived. Wild lettuce is now widely scattered over the globe, but it originated in inner Asia Minor, the trans-Caucasus, Iran, and Turkistan.
According to Herodotus, lettuce was served on the tables of the Persian kings of the 6th century B.C. In the 5th and 4th centuries B.C., other great Greek writers described and praised its virtues.
Lettuce was popular among the Romans about the beginning of the Christian Era, and had been brought to a fairly advanced state of culture and improvement. In the first century after Christ Roman writers described a dozen distinctly different sorts, some of which were fairly common.
Common garden lettuce (L. sativa) was known in China in the 5th century, if not earlier. In addition, a form of "stem lettuce" is native to China. The so-called asparagus lettuce and others with long, narrow leaves and tall, thick, succulent, edible stems are of this type. They are grown in America only as curiosities.
As in the development of the cabbages, the primitive forms of lettuce were loose, leafy, and sometimes "stemmy" types; the looseheading and firm-heading forms occurred much later.
Cos lettuce (romaine) forms an erect, compact rosette of elongated leaves, approaching the character of a head. It is relatively tolerant to heat and evidently was developed in a moderately warm climate. The old records and its name indicate an Italian origin.
Light-green, dark-green, and red-spotted forms of romaine were described in 1623. The type was common in Italy in the Middle Ages and is said to have been taken to France from Italy in 1537 by Rabelais. Toward the end of the 16th century it was still rarely grown in France and Germany. It is grown to a minor extent in America, but deserves more attention for home gardens.
Firm-heading forms had become well developed in Europe by the 16th century, but when they first were developed is unknown. The oak-leaved and curled-leaf types, and various colors now known, were all described in the 16th and 17th centuries in Europe.
Columbus evidently carried lettuce to the New World, for its culture was reported on Isabela Island (now called Crooked Island) in the Bahamas in 1494. It was common in Haiti in 1565. When it was introduced into South America is not known , but it was doubtless soon after the discovery. It was under cultivation in Brazil before 1650.
Lettuce was doubtless among the first garden seeds sown in every European colony on this continent.
Loose-leaf lettuces are still popular for home gardens because they are so easy to grow. Since, however, the loose-leaf form is highly perishable after harvesting, it is now rarely grown in the United States for sale except in greenhouses.
Most of our present commercial lettuce is of one strain or another of the New York variety or of the several Imperial strains. Although they differ in adaptability and behavior in the field, these Imperial and New York strains appear much alike to the final consumer. They are erroneously called "Iceberg" lettuce. Iceberg is a variety with red-tinged leaves and no commercial importance.
Disease-resistant Strains Developed
One of the outstanding plant-breeding accomplishments of modern times is the development of the Imperial and related strains of lettuce. These were developed for resistance to mildew and brown blight, diseases that were rapidly wrecking the huge lettuce industry of the Southwest about 15 to 20 years ago. Now nearly all of the lettuce grown in the Southwest is of these Imperial strains. Generally they are not well adapted to the East or South.
Lettuce is an annual plant that requires a relatively cool climate for good leaf and head growth. Hot weather causes it to become bitter and hastens the elongation of its stem into a tall seed stalk. The stems or "cores" of head varieties elongate too soon if grown in too warm weather, either preventing heading or causing the heads to be loose and of poor quality. Head lettuce is exacting in its climate, soil, and cultural requirements.