Quantitative Studies in Early Ovule and Fruit Development: Developmental Constraints in Balsamorhiza sagittata and B. hookeri

Abstract

In this study, developmental constraint was estimated by the correlation matrices for three developmental stages for achenes and ovules for two plants in two species of Balsamorhiza, B. sagittata and B. hookeri. Two comparisons were made, a statistical test of the equality of correlation matrices for contiguous stages of development and a graphic comparison of variable interrelationships for each stage of development for each individual plant. Individual instances of both developmentally related changes and stasis in correlation matrices were encountered more often in achenes than in ovules and in B. sagittata more than in B. hookeri. Based on these results, the concept of developmental constraints seems to refer to a specific relationship among variables at any one time as well as the way that relationship changes with time. In this context, developmental constraints may form the intrinsic "rules" that organisms follow as they develop. In formal explanations of evolution and ontogeny, developmental constraints--the "rules"--are part of the premises and cannot be a causal agent. In other words, the rules of a developmental "grammar" do not, by themselves, provide a full explanation for the "language" of morphogenesis. In the view that the increasing complexity accompanying development reflects the dissipation of energy into the characteristic form of an organism, the primary causal agent of development may be the second law of thermodynamics.