From leaf to flower: revisiting Goethe's concepts on the ¨metamorphosis¨ of plants

goethe？s seminal scientific work, versuch die metamorphose der pflanzen zu erklaren (an attempt to interpret the metamorphosis of plants) dated from 1790, has created the foundations for many domains of modern plant biology. the archetypal leaf concept, which considers floral organs as modified leaves, besides being the best known has been proven true, following the description of the abc molecular model of floral organ identity determination during the last decade. here we analyze the whole theoretical frame of goethe？s 1790 publication and present two previously misconsidered aspects of this work: the "refinement of the sap" concept as a directional principle and the "cycles of contractions and expansions" as cycles of differential determination of the shoot apical meristem. the reinterpretation of these concepts are in line with the modern view that molecular networks integrate both environmental and endogenous cues and regulate plant development. this reassessment also helps to elaborate a theoretical frame that considers the evolutionary conservation of the molecular mechanisms that regulate plant development.