Among the many interests of Swiss philosopher Jean-Jacques Rousseau (1712-78) was botany. These letters ‘addressed to a lady’ came to the attention of Thomas Martyn, professor of botany at the University of Cambridge, who thought that ‘if [they were] translated into English, they might be of use to such … as wished to amuse themselves with natural history’. However, when the translation was done, he ‘perceived that the foundation only being laid by the ingenious author, it could be of little service, without raising the superstructure’. Martyn’s 1785 publication, of which we have reissued the 1791 third edition, adds notes and corrections to Rousseau’s original thirty-two letters which explain the structure of plants and their ordering in the Linnaean system. Martyn urges the reader not to study it ‘in the easy chair at home’: it ‘can be no use but to such as have a plant in their hand’.