cloth, straw or such like." Once the seedlings emerged, the beds were "opened when the day is warmed with the sun beams" and covered at night until the danger of cold nights passed.7

The growth of protected gardening, however, proceeded slowly while a means was found to conserve heat and shelter the plants without bloc king the necessary light. Claude Mollet, gardener to Louis XIII (who reigned from 1610 to 1643), was presumably the first to mention the use of frames which were heated by manure and evidently covered with glass panes.8 Forcing frames were also noted by Andre Mollet in 1650, Winchester in 1660, and van der Groen in 1670.9 In 1690, de la Quintinye commented on the use of (1) "glassed frames" and glass bells to cover hot beds for a wide variety of vegetables and small fruits, and of (2) square glass frames with di mensions of 6 to 7 feet to warm or force fig trees.10 Just when glass was first utilized is not certain, but bell jar coverings were probably used before panes in frames (lanterns without bottoms were also used to cover plants).1

Forcing subsequently moved into wider use in England and France. Amherst notes that "enterprising gardeners. . .began to make attempts at forcing greens and salads, asparagus, and cucumbers" in England in the 1700's. Samuel Collins in 1717 wrote a treatise on the culture of melons and cucumbers, suggesting various glasses and frames for their protection.12 Similar discussions were presented by Bradley and by Miller in 1731. 13 Kalm, a Swedish horticulturist who passed through England in 1748, described some gardens where the beds were "covered with glass frames which could be taken off at will." Vegetables most numerous around London in May of that year were beans, peas, cabbage, leeks, chives, radishes, lettuce, asparagus, and spinach.14 Market gardeners in France began to sell early vegetables from forcing frames around 1780. 15

Glass was not the only covering material at this point. In the 1700's, oiled paper was used to cover portable wooden frames in England. The frames were generally 5 to 6 feet wide and the distance between the supporting hoops not more than a foot. A paper called Dutch wrapper was used and generally only lasted one season. One of the two basic frame models was designed with a hinged side. It is not clear whether manure was used as a heating agent.16

Other forms of heat began to come into use for more exotic crops and

Plate 2— At top, glass lanterns used to cover plants in the 1600's. At bottom, earliest known published drawing of vegetables growing in a frame covered with glass (Holland, 1670).

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