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Cubism began between 1907 and 1911. Pablo Picasso's 1907 painting Les Demoiselles d'Avignon has often been considered a proto-Cubist work. Georges Braque's 1908 Houses at L’Estaque (and related works) prompted the critic Louis Vauxcelles to refer to bizarreries cubiques (cubic oddities). Gertrude Stein referred to landscapes made by Picasso in 1909, such as Reservoir at Horta de Ebro, as the first Cubist paintings. The first organized group exhibition by Cubists took place at the Salon des Indépendants in Paris during the spring of 1911 in a room called 'Salle 41'; it included works by Jean Metzinger, Albert Gleizes, Fernand Léger, Robert Delaunay and Henri Le Fauconnier, yet no works by Picasso or Braque were exhibited.

Who mentioned the landscapes made by Picasso in the first Cubist paintings?
Gertrude Stein