By the middle of the nineteenth century it was as though all buildings were made of glass. In domestic treatises and encyclopaedias in Britain in particular, houses and gardens are described in terms of their formal 'character'. These terms, derived from eighteenth-century natural history, persisted in an age of biology and are particularly revealing. Consider the reflections on gardening in 1654 by Sir Hugh Platt in a treatise published in several editions during the mid-seventeenth century. Given the popularization of science, particularly in the second half of the nineteenth century, the language of forms, functions and appearances was a means whereby knowledge of the necessities of domestic life was acquired by ordinary people. Underlying the transformation of ideas about nature in John Claudius Loudon's day were scientific practices aimed at determining the 'true' or essential qualities of living beings, plants and animals. The chapter also presents an overview of the key concepts discussed in this book.