calligraphic style of the Buddhist sects known as Zen in Japan and Ch'an in China. This calligraphic form sprang directly from the transplantation during the 12th and 13th centuries of Ch'an Buddhism to Japan, in which country it became known as Zen. Bokuseki became a part of the major artistic flowering associated with Zen Buddhism during the Muromachi period (1338–1573), at which time calligraphy was regarded as an essential cultural accoutrement of a distinguished Zen monk. Bokuseki characters were written with the brush in a bold and assertive style. They often comprise a phrase or evocative saying written by a Zen master to educate his disciple or please an important visitor. Many such works eventually became highly valued collector's items, appreciated both for their aesthetic appeal and for their historical associations. The most admired bokuseki in Japan were produced by the Zen monks Musō Soseki (1275–1351), Sesson Yūbai (1290–1346), and Tesshū Tokusai (fl. 1342–66).