Morphogenesis of the spikelets and inflorescence of Andropogon gerardii Vit. (Gramineae) and the relationship between form, information theory, and thermodynamics

Abstract

The spikelets of Andropogon gerardii occur in pairs, one sessile and one pedicellate. The first glume of the sessile spikelet is bikeeled. The fertile lemma of the sessile spikelet is awned and the awn develops after the lemma has been initiated. The paleas of both spikelets initiate at two positions, are bikeeled, and, on occasion, are two-parted as a result of an interrupted zone of initiation. Each functional lodicule of A. gerardii is developmentally similar to one keel of the palea that has become thickened as a result of activity of an adaxial meristem. The spikelet pairs develop from one primordium. At early stages, spikelet pair primordia about each other along the inflorescence axis and the spikelets of a pair are not separated by a pedicel. The pedicel and the axis of the inflorescence develop through intercalary growth. Differences between appendages in the spikelet of A. gerardii can be viewed as the result of differing amounts of developmental activity (apical growth, marginal meristem, adaxial meristem) common to phyllomic structures. These common developmental activities are, in turn, the result of certain patterns of cell division and cell growth. The evolution of form thus results from alteration of common developmental events. When viewed in such a manner, the evolution of form is seen to be the modification of the informational entropy in an organism. With evolution, there are increases and decreases in informational entropy but, generally speaking, more complex organisms have higher entropy.