1. Banks HP (1975) Reclassification of psilophyta. Taxon 24:401–413
2. Bierhorst DW (1971) Morphology of vascular plants. Macmillian, New York
3. Bower FO (1958) The origin of a land flora. Hafner, New York
4. Breidbach O (2006) Goethes metamorphosenlehre. Wilhem Fink Verlag, München
5. Breidbach O (2007) Ernst Haeckel. Bildwelten der Natur. Prestel Verlag, München