This book is a compilation of 11 papers that were presented at the Twelfth Growth Symposium, which was held at the University of New Hampshire on June 14 to 22, 1953, under the joint auspices of the Society for the Study of Development in Growth and the Committee on Developmental Biology of the National Research Council. The topic for this Symposium was "Biological Specificity and Growth" and the broadness of the subject was such that the subjects discussed varied from problems of specificity in the sexuality of plants, as presented by John Raper, to a discussion of host-parasite relationships by W. H. Taliaferro.