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Science 26 June 2009:
Vol. 324. no. 5935, pp. 1652 - 1653
DOI: 10.1126/science.1176526
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Perspectives

Evolution:

Auxin at the Evo-Devo Intersection

William E. Friedman

"Alles ist Blatt." With this simple but profound assertion ("All is leaf "), Johann Wolfgang von Goethe launched the modern age of comparative biology (1–3). By articulating the concept that plants can be broken down into modular and iterative variants of an archetypal structure (the leaf, in the form of bud scales, spines, petals, stamens and so forth), Goethe propelled the analysis of plant and animal structure (4) for the next two centuries and beyond. The idea that variant forms of a basic organ "type" are homologous (morphologically equivalent) within an organism and between organisms has emerged as a central conceptual (and testable) framework in the burgeoning field of comparative molecular analyses of development. On page 1684 of this issue, a study by Pagnussat et al. (5) brings together a remarkable set of experiments that bear on the developmental biology and modular construction of the microscopic egg-producing structure (female gametophyte or embryo sac) buried deep within a flowering plant's reproductive tissues. The findings have great importance for understanding and further examining the evolutionary developmental history of flowering plants.

Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA.

E-mail: ned{at}colorado.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)