Auction introduction: Christie’s next auction of Modern American Art on 18 April will feature a strong selection of early 20th century painting, drawing and sculpture. Leading the sale is Milton Avery’s vibrant Female Painter of 1945 along with other significant paintings by Thomas Hart Benton, Charles Burchfield and Fairfield Porter. A stunning selection of still-life painting includes Georgia O’Keeffe’s Blue Morning Glory and Florine Stettheimer’s Tulips Under a Canopy. American Illustration will also be highlighted with Maxfield Parrish’s masterwork Ottaquechee River, two works by N.C. Wyeth, and Saturday Evening Post covers by Norman Rockwell and others.