A reproduction of a Thesis in partial fulfillment of the Degree of Master of Science, University of Auckland. The research was carried out on three viruses found to infect Vanilla fragrans in the Kingdom of Tonga. It is now known that two of the viruses are present in all countries that grow orchids but the most devastating one appear to be of limited distribution in the Pacific Islands. This is the black and white copy. If your search cannot locate the colour copy try messaging amazon!