In this article we will discuss about:- 1. Meaning of Photoperiod 2. Photoperiodic Response Groups 3. Photoinductive Cycles 4. Genetic Approach 5. Flowering Hormone. Subject-Matter of Photoperiod: Two American plant physiologists, W.W. Garner and H.A. Allard (1920) while working at the USA department of Agriculture Research Laboratories at Beltsville, Maryland made observations that tobacco variety, […]