X PREFACE 



Laboratory, and the Botany Department of the University of IlHnois for 

 the patience with which they have allowed him to use their facilities for the 

 completion of this work. The author owes much to discussion with his 

 co-workers, Dr. A. Stanley Holt and Dr. E. E. Jacobs. Mr. Paul Latimer, 

 Mr. John Coleman, and Dr. Sylvia Frank have helped in the preparation 

 of the index. Miss Natalie Davis kindl}^ supplied one of the drawings. 



Miss Carolyn Prouty has helped to minimize, in this volume, the vexa- 

 tious errors in bibliography, much too many of which have been permitted 

 to go undiscovered in Volume I : she and Mrs. Ruth Adams have also helped 

 with proofreading. Interscience Publishers have shown infinite patience 

 and forbearance with the author's unreliability, procrastination, and 

 tendency to enlarge and change the text up to the very last moment. The 

 author's warm thanks are due Dr. Eric S. Proskauer and his staff. 



The author early acquired a prejudice against dedicating scientific treat- 

 ises to parents, teachers, or wives; it somehow seemed to him that such 

 homage should be reserved to more personal works of art, and those who 

 inspired them. This prejudice has prevented him from expressing his 

 thanks to the one man to whom he owes both his interest in photochemistry 

 and photobiology, and whatever special qualifications he may have to deal 

 with these subjects, in the most natural and adequate way — by dedicating 

 this monograph to him. The author has had the privilege of studying or 

 working with several great scientists of our time; but Dr. James Franck is 

 the one of whom he likes to consider himself a pupil — not only in the nar- 

 rower field of common scientific specialization, but in the whole approach 

 to the world of atoms and molecules. While the author has not been able 

 to match the persistence, concentration, and clarity of thinking that have 

 made James Franck one of the great pathfinders in this enchanted world (not 

 to speak of acquiring his humility and deep understanding of the world of 

 men), he can plead that these have been among the strongest influences he 

 has experienced, and guiding lights he has tried to follow. 



I hope Dr. Franck will accept these words of gratitude at the end of the 

 long work, in lieu of a dedication which was due to him on its first page. 



Eugene I. Rabinowitch 

 Urhana 

 April 1956 



