This volume is a sequel to the two introductory volumes (1980, 1983) to the second edition of Anatomy of the Dicotyledons, of which the first edition appeared in 1950. It is the first in a series in which the comparative structure of the leaf, stem, and wood is to be described, as a contribution to the classification of the families of dicotyledons. The ecological significance of some of the characters is also discussed. The present volume covers twenty families that are generally accepted as fairly close relatives and are of special interest because of their alleged primitive status in the hierarchy of plant families. Much information has become available about these families since the first edition was published, either in scattered publications or through original observations at Kew. The text relating to these families has accordingly been completely rewritten and expanded. The volume contains a wealth of newly prepared photographs and a comprehensive bibliography.