THE ALLOMETRY OF PLANT REPRODUCTIVE BIOMASS AND STEM DIAMETER

species, however, were M = 0.46D46 (r2 = 0.99, N = 41), M = 0.07D32 (r2 = 0.91, N = 65), M = 0.56D22 (r2 = 0.92, N = 85), and M = 0.44D1 8 (r2 = 0.97, N = 21), respectively, indicating that the proportionality M oc D--30 recedes with finer taxonomic resolution. The data for Cooksonia were found to comply with the allometry of Polytrichum when the regression curve of this moss was extrapolated into the size range of the fossil species. Analyses showed that intraspecific allometric scaling factors a were dependent upon the manner in which plant stems taper. Species or portions of branching systems with a > 4.0 had essentially untapered stems (e.g., Polytrichum commune, Psilotum nudum, twigs of Larix decidua); species with a < 2.2 had tapered stems resulting from secondary growth in most cases. The evolution of tapered primary stems and secondary growth was interpreted to alter reproductive allometry. This paper provides intra- and interspecific allometric descriptions of the relation between reproductive biomass and stem diameter for a total of 12 extant moss, pteridophyte, and gymnosperm species. Comparable descriptions are provided for the fossil remains of the early Paleozoic vascular plant remains of the rhyniophyte Cooksonia pertoni and the trimerophyte Psilophyton princeps. Quantitative descriptions of the relation between biomass and plant size provide useful rules to estimate the allocation of resources to reproductive, mechanical, and other functions. General allometric relations for this purpose are available for species of angiosperm trees (Murray, 1927; Whittaker and Woodwell, 1968; Mc