plants in the late 1600's. Stoves were probably first used for conservatories (orangeries).17 In 1684, it was noted that a Mr. Watts, gardener at Apothe caries Garden in Chelsea, heated a greenhouse from below with a flue system; this was known as a dry stove.18 Bark stoves, which provided a moderate moist heat, were probably first developed in Holland after 1600; in the early 1700's, they were used for the cultivation of pineapple.19

At first, the greenhouse of the 1700's used glass on one side only in the form of a sloping roof. Later in the century, glass was used for the front and on both sides of lean-to houses. The two-sided greenhouse emerged through the 1800's,20 but was seldom used for vegetable production. The vast bulk of vegetables continued to be raised in the more prosaic manure-heated frame.

Plate 3— Typical heated greenhouses of the late 1700's, showing arrangement of heating flues. At the time, these structures were known as forcing houses or hot walls. (England, 1789.)

By the late 1700's and early 1800's, the forcing of food crops was a subject of a number of books in England.21 The technique, however, was initially limited to private estates, and consumption of the produce was confined to the wealthy. Around the middle of the 1800's, greenhouse products such as grapes, melons, peaches, and strawberries began to arrive on English markets. Green house tomatoes did not appear until the 1870's and did not begin to become popular until the 1880's. Important early greenhouse areas included, roughly in chronological order, Guernsey, Worthing, North London and Lea Valley, Swanley, and Blackpool. Four tons of Guernsey grapes were sold in Covent Garden in 1856. Worthing had about an acre of greenhouses by 1870 and

-10-