Crafts et al. — viii — Water in Plants 



operation, and his studies must deal with the description as well as the 

 mathematical aspects of its functioning. Ultimately, all these problems must 

 submit to analysis in terms of the molecular mechanics of the systems in- 

 volved. 



With regard to the above problem, we hope that this volume will serve 

 two purposes. For plant workers, we trust that it will develop an apprecia- 

 tion for the exact analytical methods of the physical sciences. Much of the 

 progress in the field of water relations has resulted from use of such methods. 

 For the physical chemist, on the other hand, we hope to have presented a 

 challenge to broaden, if need be, his view of the physical universe to en- 

 compass those many living systems upon which his very existence depends. 

 There should be some common ground where these two may meet to work 

 out their common problems for the mutual benefit of all. And if such co- 

 operation between fundamental and applied scientists will lead to a warmer 

 feeling of appreciation by both for their common interests, much good will 

 have been done. The field of plant water relations presents many problems 

 upon which such cooperative effort may be profitably spent. We hope that 

 our volume may present these problems in such a way that many workers 

 will be stimulated in their study. 



In conclusion, we would like to express our appreciation to our many 

 friends who have contributed to the writing of this monograph. Through 

 conferences, discussions, and, in some instances, almost daily contacts, they 

 have helped clarify some of the intricate problems involved in plant water 

 relations. For reading parts of the manuscript we are especially indebted 

 to Dr. L. E. Davis ; for use of manuscripts, which at the time of writing 

 were not yet published, we thank Dr. B. S. Meyer and Mr. T. C. Broyer ; 

 for counsel and advice in the development of the concepts of osmosis and 

 osmotic pressure we express our appreciation to Drs. N. E. Edlefsen, 

 F. A. Brooks, Max Kleiber, H. A. Young, H. G. Reiber and R. B. 

 Dean. Translations of many foreign papers were kindly put at our dis- 

 posal by Dr. F. J. Veihmeyer and Mr. T. C. Broyer. For encourage- 

 ment throughout the preparation of the manuscript and aid in its final or- 

 ganization we are grateful to Dr. W. W. Robbins. 



This book has been produced during troubled times. Because publication has 

 been delayed, many current papers are not cited in the text. Some of these we are 

 reporting here in an effort to bring our Bibliography up-to-date. 



Workers on the properties of liquids and solutions are in general agreement that 

 the unusual behavior of water results from coordination of its molecules by hydrogen 

 bonding. Assuming a bonding energy of 4.25 K cal. per mole, Taft and Sisler (1947) 

 calculate that, of the energy absorbed upon heating, 11 per cent is utilized in breaking 

 bonds during melting of ice, 16 per cent is used raising the temperature from the 

 melting to the boiling point, and "JZ per cent goes in the vaporization process. 

 Weissler (1949), using the velocity of sound at different temperatures to determine 

 coordination, concludes that water undergoes a decrease in association of about 7.2 

 per cent between 0°C. and 100° C. Sound waves will detect molecular aggregates that 

 are stable for 10"*^ seconds. A previous value of 13.2 per cent was found using Raman 

 spectrum analysis. The difference is due to the fact that the latter method detects 

 aggregates that are stable for only lO"'^'* seconds. 



In contrast to Taft and Sisler, Searcy (1949) calculates a value of 6.4 ± 0.5 

 K cal. for the H-bond energy in water. He concludes that repulsive as well as at- 

 tractive forces contribute to the dipole energy. 



Using a new formula to determine an index of association in liquids, Parshad 

 (1947) has calculated values between 240 and 325 for a series of non-polar compounds; 



