de wit was especially interested in the aroid genus "cryptocoryne", as well as the closely related "lagenandra" on which he published extensively. in all, he described 21 new species of "cryptocoryne" and 6 species of the related genus "lagenandra". a lifelong hobby were freshwater aquaria and in the late 1950s he edited an encyclopaedia for aquarists in 15 volumes, 2 of which (volumes 5 and 6) dealt with aquarium plants and were written by himself. in 1966 these volumes were revised and published together as the first edition of his book "aquariumplanten" was published. it was translated in english in 1964 and in german in 1971. after his retirement, he wrote a history of biology ("ontwikkelingsgeschiedenis van de biologie") in three volumes (1982–1989). a popularized version appeared in 1993 ("wat is leven? een cultuurgeschiedenis van de biologie").