The dean of living Russian novelists, IvAN BUNIN was born in 1870 at voronezh in Central Russia. His early work, for which he was awarded the Pushkin Prize by the Russian Academy, attracted the attention of Leo Tolstoy and Anton Chekhov, and his friendship with the latter began in 1895. Mr. Bunin has lived in exile since the Russian Revolution; now in his new book Memories & Portraits, which Doubleday is to publish this summer, he has given us a firsthand account of those Russian immortals whom he knew in his youth.