Allometry, the study of the growth rate of an organism's parts in relation to the whole, has produced various results in research on animals. This text applies allometry to studies of the evolution, morphology, physiology and reproduction of plants. The author covers a broad spectrum of plant life, from unicellular algae to towering trees, including fossil as well as extant taxa. He examines the relation between organic size and variations in plant form, metabolism, reproduction and evolution, and draws on the zoological literature to develop allometric techniques for the peculiar problems of plant height, the relation between body mass and body length, and size-correlated variations in rates of growth. For readers unfamiliar with the basics of allometry, an appendix explains basic statistical methods. This text should be useful reading for botanists interested in an original, quantitative approach to plant evolution and function, and for zoologists who want to learn more about the value of allometric techniques for studying evolution.