THE HOUSE BEHIND THE CEDARS. By Charles W. Chesnutt. 294 pp. $1.50 (Houghton, Mifflin.) A dramatic story of the color-line in Southern life. The heroine, an octoroon who "passes for white," almost succeeds, but her failure is one of the most tragic things in recent fiction. A well-constructed and well-written story of great directness and power.