Various, Encyclopaedia Britannica, 11th Edition…
“ The Greenhouse is a structure designed for the growth of such exotic plants as require to be kept during winter in a temperature considerably above the freezing-point. The best form is the span-roofed, a single span being better even than a series of spans such as form the ridge-and-furrow roof. For plant culture, houses at a comparatively low pitch are better than higher ones where the plants have to stand at a greater distance from the glass, and therefore in greater gloom. Fig. 3 represents a convenient form of greenhouse. It is 20 ft. ”
