during world war ii de wit worked in the 's lands plantentuin te buitenzorg. after his return to the netherlands in 1946 he worked for the flora malesiana foundation. de wit was a gifted teacher and on 20 september 1953 he became a lecturer at leiden university where he taught plant taxonomy and morphology of flowering plants and on 1 november of the same year also at the wageningen university and research centre, where he taught taxonomy and tropical and subtropical plant geography. in 1959 he left leiden to become full professor in wageningen and on 15 september 1969 he became the head of the laboratory of plant taxonomy and plant geography there. de wit retired in 1980, at which occasion a festschrift was published in his honour.