Vm CONTENTS 



9. Phototropism 463 



F. W . Went, Professor of Plant Physiology, California Institute of Tech- 

 nology, Pasadena, California 



10. Photoperiodism 479 



H. A. Borthwick, U.S. Department of Agriculture, Bureau of Plant Indus- 

 try, Soils, and Agricultural Engineering, Beltsville, Maryland 



S. B. Hendricks, U.S. Department of Agriculture, Bureau of Plant Indus- 

 try, Soils, and Agricultural Engineering, Beltsville, Maryland 



M. W. Parker, U.S. Department of Agriculture, Bureau of Plant Industry, 

 Soils, and Agricultural Engineering, Beltsville, Maryland 



11. Seed Germination 518 



Michael Evenari, Professor of Botany and Plant Physiology and Vice 

 President of the Hebrew University, Jerusalem 



12. Viscosity, Permeability, and Protoplasmic Streaming 551 



M. G. Stalfelt, Professor of Plant Physiology, University of Stockholm, 

 Stockholm, Sweden 



13. Electrical Phenomena in Vision 581 



Lorrin A. Riggs, Professor of Psychology, Brown University, Providence, 

 Rhode Island • 



14. Invertebrate Photoreceptors 621 



Lorus J. Milne, Professor of Zoology, University of New Hampshire, 

 Durham, New Hampshire 



Margery J. Milne, Honorary Fellow in Zoology, University of New 

 Hampshire, Durham, New Hampshire 



15. Photodynamic Action and Its Pathological Effects 693 



N. T. Clare, Chief Biochemist, Ruakura Animal Research Station, 

 Hamilton, New Zealand 



Name Index 725 



Subject Index 743 



