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Hydraulic segmentation at the stem-leaf transition predicts higher hydraulic resistance in leaves than in stems. Vulnerability segmentation, however, predicts lower embolism resistance in leaves. Both mechanisms should theoretically favour runaway embolism in leaves to preserve expensive organs such as stems, and should be tested for any potential coordination. We investigated the theoretical leaf-specific conductivity based on an anatomical approach to quantify the degree of hydraulic segmentation across 21 tropical rainforest tree species. Xylem resistance to embolism in stems (flow-centrifugation technique) and leaves (optical visualization method) was quantified to assess vulnerability segmentation. We found a pervasive hydraulic segmentation across species, but with a strong variability in the degree of segmentation. Despite a clear continuum in the degree of vulnerability segmentation, eight species showed a positive vulnerability segmentation (leaves less resistant to embolism than stems), whereas the remaining species studied exhibited a negative or no vulnerability segmentation. The degree of vulnerability segmentation was positively related to the degree of hydraulic segmentation, such that segmented species promote both mechanisms to hydraulically decouple leaf xylem from stem xylem. To what extent hydraulic and vulnerability segmentation determine drought resistance requires further integration of the leaf-stem transition at the whole-plant level, including both xylem and outer xylem tissue., (© 2020 The Authors. New Phytologist © 2020 New Phytologist Trust.)

Before Vivant Denon, the dealer Jean-Baptiste-Pierre Lebrun played a crucial role in the creation of the Louvre collections, despite the revolutionary discourse which opposed the market to the museum. Lebrun's position as a polemicist is interpreted here as a strategy of self-presentation which made possible the controversial birth of the figure of the museum expert. With Lebrun, the Louvre imposed itself as a public space of artistic expertise, where values imported from the market - such as attributionism, materiality, and authenticity - became prominent in the evaluation of paintings.