developed in the studios of Picasso and Braque; the second phase being called "High Cubism", (from 1909 to 1914) during which time Juan Gris emerged as an important exponent (after 1911); and finally Cooper referred to "Late Cubism" (from 1914 to 1921) as the last phase of Cubism as a radical avant-garde movement. Douglas Cooper's restrictive use of these terms to distinguish the work of Braque, Picasso, Gris (from 1911) and Léger (to a lesser extent) implied an intentional value judgement. Proto-Cubism: 1907–1908 Cubism burgeoned between 1907 and 1911. Pablo Picasso's 1907 painting Les Demoiselles d'Avignon has often been considered a proto-Cubist work. In 1908, in his review of Georges Braque's exhibition at Kahnweiler's gallery, the critic Louis Vauxcelles called Braque a daring man who despises form, "reducing everything, places and a figures and houses, to geometric schemas, to cubes". Vauxcelles recounted how Matisse told him at the time, "Braque has just sent in [to the 1908 Salon d'Automne] a painting made of little cubes". The critic Charles Morice relayed Matisse's words and spoke of Braque's little cubes. The motif of the viaduct at l'Estaque had inspired Braque to produce three paintings marked by the simplification of form and deconstruction of perspective. Georges Braque's 1908 Houses at L’Estaque (and related works) prompted Vauxcelles, in Gil Blas, 25 March 1909, 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. By 1911 Picasso was recognized as the inventor of Cubism, while Braque's importance and precedence was argued later, with respect to his treatment of space, volume and mass in the L’Estaque landscapes. But "this view of Cubism is associated with a distinctly restrictive definition of which artists are properly to be called Cubists," wrote the art historian Christopher Green: "Marginalizing the contribution of the artists who exhibited at the Salon des Indépendants in 1911 [...]" The assertion that the Cubist depiction of space, mass, time, and volume supports (rather than contradicts) the flatness of the canvas was made by Daniel-Henry