Section of Span-Roofed Pit
A diagram consisting of a section of a span-roofed pit. These pits are useful for plant culture. A, Ordinary Soil; b, Passage; c, Heated Chambers; d, Plunging Beds; e, Hot-Water Pipes.
Nicholson, George The Illustrated Dictionary of Gardening, Div. VI (London, England: L. Upcott Gill, 1884)
Courtesy the private collection of Roy Winkelman