Buyck, F. Jean, Hugo Heyrman ‘Pictor Ecologicus’. Originally published as introduction to the retrospective exhibition of Hugo Heyrman’s paintings in the Antwerp Royal Museum of Fine Arts (1984, October 13 - December 9).
Translated from Dutch by Joris Duytschaever. http://www.doctorhugo.org/paintings/bibliography/pictorecologicus.html