The investigation forming the subject of this report was planned to study certain factors affecting Botrytis diseases on certain crop plants. Results are summarised in the following points: 1. The optimum temperature for growth of Botrytis cinerea Pers., Botrytis cinerea f. lini, Botrytis fabae Sard., Botrytis galanthina Berk. & Br., Botrytis narcissicola Kleb., Botrytis paeoniae Oudem. and Botrytia squamosa Walker was 21