Later he was assistant at the Botanical Museum and Herbarium, Berlin-Dahlem, on 1 October 1920, the beginning of an uninterrupted career at that institute in which he went through all the ranks, ending as interim director (1958–1959), and having been professor of botany from 1940 teaching at Technical University of Berlin.
Among his many contributions to taxonomy are his treatments of the Medusagynaceae, Theaceae, Violaceae, and Canellaceae for the second edition of the Die Natürlichen Pflanzenfamilien of Engler & K. Prantl, the publication as editor with E. Werdermann, of ed. 12 (1954-1964) of Engler's "Syllabus der Pflanzenfamilien", and, as a last major contribution (with Hans Kastner) of Gewurze (1974).
His main interest was in the Violaceae, Theaceae, and Bignoniaceae and, especially in his earlier years, in the flora of the Alps. He received his introduction to this flora in his excursions as a student with Engler, retained the best possible memories of these events, and attributed to them the awakening of his interest in plant systematics. Melchior was a founding member of I.A.P.T. and stayed in this institution until his death.
- Taxon, Vol. 33, No. 3 (Aug., 1984), p. 560.