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Plant Allometry. The Scaling of Form and Process. KARL J. NIKLAS. University of Chicago Press, Chicago, 1994. xvi, 395 pp., illus. $62.50 or L49.95; paper, $24.95 or L19.95.
Allometry--the change in shape, metabolism, or behavior with body size among related organisms--is surely one of the most fascinating phenomena in biology. As first recognized by Julian Huxley in the 1930s, allometry is a pervasive pattern in the fabric of life. Among animals, increases in body size bring fairly regular shifts in the relative size of brains, antlers, guts, and limb-bone diameters, in basal metabolisms, pulse rates, stride frequencies, and running speeds, and in food preferences, territory sizes, species numbers, and extinction rates. Interest in these zoological patterns and their causes has given rise to a spate of publications including two fine books (by Calder and Peters) in recent years. But until now no one has attempted to summarize and analyze the parallel patterns seen among plants.
Niklas makes the first such attempt in this wide-ranging book. Plants span a huge size range (from picoplankton to sequoias) and encompass a multiplicity of functions (mechanical support, photosynthesis, nutrient and water absorption) whose magnitude and integration must shift with size. Niklas begins by presenting 39 allometric relationships, or scaling laws, shown by plants or plant organs that vary in size and then discusses the possible significance and biological basis of each through the rest of the book. The patterns cover a wide sweep of botanical phenomena, and several are novel (but identified on the basis of limited data). Among unicellular algae, growth rate and chlorophyll concentration scale as roughly the 0.75 power of cell volume, while surface area scales as the 0.68 power. Leaf area is proportional to roughly the square of twig diameter. Stem diameter scales approximately as the 1.5 power of height in trees, but as the 0.75 power of height across mosses, herbaceous plants, and palms. The relative investment in stamens and in pistils and ovules increases with flower size; total seed mass increases proportionally to fruit...