Irving W. Bailey and Ralph H. Wetmore initiated the wood collection through their interests in plant structure and its relationship to systematics and evolution. Together they assembled a collection that now includes more than 33,000 wood specimens (including fossils) from more than 300 families from around the world, and over 50,000 microscope slides of wood and of other plant parts. These form an exceptionally rich source of information for the study of plant form and structure. The collection represents a valuable addition to the other plant collections maintained at the Harvard University Herbaria.