In 1967 he became chairman of the SPD group in the Landtag , and in 1970 Minister of Science and Education in the cabinet of Minister President Heinz KÃ 1\/4 hn . In 1967 , he became chairman of the SPD fraction in the Landtag , and in 1970 Minister of Science and Education in the cabinet of Minister President Heinz KÃ 1\/4 hn .