1. Ahmadjian, V. and Paracer, S. (1986) Symbiosis. An Introduction to Biological Associations, University Press of New England
2. Sapp, J. (1994) Evolution by Association. A History of Symbiosis, Oxford University Press
3. Smith, D.C. and Douglas, A.E. (1987) The Biology of Symbiosis, Edward Arnold
4. Khakhina, L.N. (1992) in Concepts of Symbiogenesis: A Historical and Critical Study of the Research of Russian Botanists (McMenamin, M. and Margulis, L., eds), Yale University Press
5. Chapman, M.J. and Margulis, L. Int. J. Microbiol. (in press)