Abstract: A greenhouse structure made of glass panels and having spaced parallel rails for supporting the structure, the glass panels being attached and supported at the upper portions of the rails, and a second set of transparent panels made of plastic material, the panels of the second set being attached and supported at the lower portion of the rails. The invention includes a special construction in which the rails have rims and a strip of plastic material extends about the lower part of the rails and engages a rim on the rail, this plastic material providing a pair of lips which receive the edge of the plastic panels.The invention also includes methods of assembly in which a plastic panel is bowed to shorten the distance between the side edges of the panels so that it may be positioned between rails and then relaxed to cause the edges of the panel to snap into place between the lips of the plastic strip which is carried by each of the rails.