The production of a physiological puzzle: how Cytisus adami confused and inspired a century's botanists, gardeners, and evolutionists.

'Adam's laburnum' (or Cytisus adami), produced by accident in 1825 by Jean-Louis Adam, a nurseryman in Vitry, became a commercial success within the plant trade for its striking mix of yellow and purple flowers. After it came to the attention of members of La Société d'Horticulture de Paris, the tree gained enormous fame as a potential instance of the much sought-after 'graft hybrid', a hypothetical idea that by grafting one plant onto another, a mixture of the two could be produced. As I show in this paper, many eminent botanists and gardeners, including Charles Darwin, both experimented with Adam's laburnum and argued over how it might have been produced and what light, if any, it shed on the laws of heredity. Despite Jean-Louis Adam's position and status as a nurseryman active within the Parisian plant trade, a surprising degree of doubt and scepticism was attached to his testimony on how the tree had been produced in his nursery. This doubt, I argue, helps us to trace the complex negotiations of authority that constituted debates over plant heredity in the early 19th century and that were introduced with a new generation of gardening and horticultural periodicals.