Plant Physiology lucidly explains the operational mechanisms of plants based on up-to-date literature and with the help of numerous illustrations. In addition to the theoretical aspects, experiments have been incorporated at the end of relevant chapters. The fourth edition has been updated and thoroughly revised in the light of the UGC model curriculum. Amendments and fresh inclusion are particularly evident in the chapters on Cell Structure and Functions, Elementary Biochemistry, The Enzymes, Photosynthetic Apparatus, Photosynthesis, Photorespiration, Respiration, Plant Growth Regulators, Biological Clocks, and Role of Plant Physiology in Agriculture. New chapters on Photobiology, Photomorphogenesis, and Senescence and new topics like Calmodulin, Cryptochrome, CAMP, and Signal Transuduction Mechanism have been included to provide wide coverage of the subject. The presentation and illustrations have been considerably improved. The book, with its compilations of vast literature and its lucid presentation, will certainly be useful to undergraduate and postgraduate students. It will also be of help to students preparing for various competitions, including IAS, PCS and Medical Entrance Examinations of various boards.