"There is a remarkable painting in the Picasso room at Kunstmuseum in Basel: a full-length portrait of Guillaume Apollinaire with his muse, Marie Laurencin. It was Henri Rousseau who painted this wonderful picture. Only I had remembered it as a self-portrait of Rousseau with Madame Rousseau. Marie Laurencin was Apollinaire's muse, and Cl mence Rousseau was Rousseau's muse. As it happens, Franz Marc painted a portrait of Rousseau for Der...