In Britain in the closing years of the eighteenth century, two significant shifts in glasshouse design both reflected and facilitated a decisive change in the relationship between the house and its landscape setting. The first was a profusion of glazed conservatories attached directly to the main residence of country estates, serving as both social and botanical spaces that—unlike their free-standing counterparts—were immediately accessible from adjacent polite rooms of the house. The second development of especial interest was that, although most of these conservatories were rectilinear, a number of them were designed in a quadrant shape, typically with glazing on their concave façade. Largely overlooked in scholarship to date, these two interrelated phenomena are examined in the work of leading architects of the period, with particular attention to the role of landscape gardener Humphry Repton. An investigation of possible precedents and reasons for utilising this form leads to the conclusion that, rather than being chosen primarily for horticultural reasons, the attached quadrant conservatory served above all to embody late-eighteenth-century Picturesque ideals of asymmetry, movement and imagination.