'Photoperiodism and vernalization are fascinating areas in plant physiology. The phenomena were conceived as the expedients to switch on flowering in plants but with passage of time, divulged intricacies establishing as exponents to a wider range of functional processes in them. Despite much of the complexities on the living processes in plants have been discovered by delving into these areas, much remains to be unravelled. The present title has brought forward the diverse features of these disciplines to the students and buding scientists of plant physiology in a simplified form to arouse their interest and gain ground for deeper understanding into these spheres.' Contents: Part I: Photoperiodism Chapter 1: Physical Aspects of Light and its Role in Plants; Physical aspect of light; How light affect plants; Chapter 2: Photoperiodism; Historical aspects; Definition and concept; Photoperiodic groups of plants; Maturity of plants for photoperiodic responses; Requirement of the number of photo inductive cycles; Photoperiodic induction; Site of perception of photoperiodic stimulus; Role of dark and light periods in photoperodic cycles; Role of light quality and phytochrome; Time measurement by plants; Mechanism of photoperiodism; Genetic approach of photoperiodic response in plants; Photoperiodic effects other than flowering; Practical utilization of photoperiodism; Review of terminology. Part II: Vernalization Chapter 1: Physical Aspects of Heat and its Role in Plants; Physical aspect of heat; How heat affect plants; Chapter 2: Vernalization; Historical aspect; Definition and concept; Quantitative and qualitative responses; Examples of vernalizable seeds and plants; Site of perception of vernalization stimulus; Maturity factor in vernalization; Technique of vernalization of seeds and other plant parts; Induction of vernalization effect; Reversibility of vernalization response; Mechanism of vernalization; Genetic approach of vernalization; Practical utilization of vernalization; Relationship between vernalization and photoperiodism.