In 1880 the director of the Royal Botanic Gardens at Kew described a botanic garden as a garden in which a vast assemblage of plants from every accessible part of the Earth's surface is systematically cultivated. By then botanic gardens had existed in Europe for over three and a quarter centuries, had established themselves as an acceptable part of the urban environment, and become the recipients of a flood of vegetation from overseas. By the time of Queen Victoria's death in 1901, botanic gardens were an integral part of empire and four of the greatest of them - those at Calcutta, Pamplemousse on Mauritius, Peradeniya on Ceylon and Trinidad - carried the prefix Royal Botanic Gardens. This book is a thematic history of the imperial network of these gardens which had its informal centre at Kew.