Three major changes have been made in Research Experiences in Plant Physiology in producing this second edition. The format has been changed so as to minimize the number of pages and hence the cost to students, hopefully without sacrifice of readability or general utility of the manual. Three new exercises have been added on Phytochrome Effects in Nyctinastic Leaf Movements (Exercise 26), Measurement of Leaf Water Potentials with a Pressure Chamber (Exercise 27), and The Hill Reaction of Photosynthesis (Exercise 28) in an effort to provide more balanced coverage of the major topics in Plant Physiology. Lastly, modest revisions have been made in the text and lists of references throughout the manual and in the index. It is hoped that these collective changes will lead to continued wide acceptance of Research Experiences in Plant Physiology as the laboratory manual for upper-division undergraduate and graduate courses in Plant Physiology. The preparation of this new edition naturally has involved the invaluable assistance of several persons. lowe special thanks to Mrs. Ellen Witt for her patience and proficiency in retyping the entire manual. To Mrs. Witt, Mrs. Leona Nicholson, and my wife, Arvida, I am grateful for assistance in proofreading. I thank Brian D. Cleary for assisting with the writing of Exercise 27 on leaf water potentials, and Donald J. Armstrong for his valuable criticism and suggestions regarding many of the exercises. Finally, I thank Mr. Stephen J. Danko for assisting with the testing of the new exercises. Thomas C.