II. HISTORICAL DEVELOPMENT

The greenhouse as we know it dates back to the early 1800's. But several of its key features— the use of transparent covering and the provision of heat— are much older. They were first mentioned in Roman times and emerged again in more advanced form during the Renaissance in Europe. European develop ments in turn were transferred to the United States, where further improve ments were introduced. By the late 1800's, greenhouse vegetable production had become a commercially important enterprise in America, England, and France.

These developments are discussed below. More recent advances in green house construction and the development of other methods of environmental control are reviewed in chapter III. Developments in individual nations during the 20th century are noted in chapter IV.

ROMAN PRACTICES

The Roman Emperor Tiberius Caesar (who ruled between 14 and 37 A.D.), reportedly told by his doctor that he needed a cucumber a day, had arrange ments made to produce them nearly the year round.1 Moveable beds were placed outside on favorable days and inside during inclement weather. Ac cording to Pliny, on wintry days the beds were covered by frames glazed with transparent stone.2 This was done "so that. . .when days were clear, they may be safely brought out into the sun."3 Among the transparent stones (specu- laria) used were those formed in slate-like plates such as mica, alabaster, and talc.4 While Columella recommended the use of well-manured soil, it is not clear whether he had its heat-producing qualities in mind.5 In any case, the use of such cultural methods was undoubtedly very limited and seems to have ceased, at least as far as recorded history goes, with the decline of the Roman Empire.

THE 15th TO 19th CENTURIES IN EUROPE

Nothing more is known of the precursors of the greenhouse until the beginning of the Renaissance in Europe. From the late 1500's until the 1800's, many of the present characteristics of the greenhouse began to emerge. Nearly all of the efforts recorded here were in England and France.6

The first known reference to vegetable forcing appeared in Gerarde's Herball, published in London in 1597. The role of manure in forcing early cucumbers in beds is clearly reported. Moreover, the beds were insulated: they were crossed with hoops and poles and then covered with "mats, old painted

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