Chapter I 

 INTRODUCTION 



The relation of water to plant cells is at the same time one of the oldest 

 and one of the most modern of physiological problems. Malpighi, Hales, 

 Knight, and a host of early plant scientists recognized this important field 

 of study. Survey of modern literature proves that water relations still 

 claim the attention of leading plant physiologists. Viewpoints change; 

 methods improve; still the underlying principles of water absorption and 

 utilization challenge the researcher. Almost all plant functions involve 

 water relations in some form or other; provision of adequate water for 

 maximum growth of plants is the basis of successful agriculture in many 

 parts of the world. 



Writing a concise monograph on water relations is a difficult task for it 

 involves selecting from an immense literature material relevant to modern 

 concepts and problems. To be of value, furthermore, such a monograph 

 should contain original work by the authors or it should involve synthesis 

 of new concepts from previous publications. Availability of modern ab- 

 stracting and reviewing agencies renders almost useless a mere compilation 

 or uncritical review of published articles. 



This volume aims to attain both of the above objectives ; it also attempts 

 to aid students in becoming familiar with contemporary literature in the 

 field. A balanced treatment of the subject involves a description of the 

 structure of water and aqueous solutions, a review of the concepts of the 

 mechanism of osmosis, consideration of the water relations of individual 

 cells, and finally, analysis of the functions of absorption, movement, reten- 

 tion, and loss of water by organized plants. It is obvious that space cannot 

 be devoted to a detailed historical review. Mainly as an aid to students, the 

 following introduction to source materials is included. 



Works of Malpighi (1675), Hales (1738), and Knight (1801) are of historical 

 interest only. Ideas in their time were confused by failure to clearly distinguish be- 

 tween the water relations of plants and animals. 



Discovery of the microscope stimulated interest in plant structure. The earlier 

 works on conducting systems are thoroughly covered by Strasburger (1891) and 

 Haberlandt (1914). Meanwhile Dutrochet (1827), Pfeffer (1877), van't Hoff 

 (1887 and 1888), and de Vries (1918) laid the foundations for a physical analysis of 

 cell water relations through their studies on osmosis and osmotic pressure. Work by 

 Berkeley and Hartley (1906), Morse (1914), Frazer and Myrick (1916), and 

 Berkeley, Hartley, and Burton (1919) provides a quantitative basis for such analysis. 



Theoretical treatment of osmotic systems by Lewis (1908), Haldane (1918), 

 Bancroft and Davis (1928), and others has materially broadened our concepts while 

 reviews by Findlay (1919), Meyer (1938), and Ursprung (1938) have marked 

 progress in this field. Of treatments in physico-chemical texts, those of Washburn 

 (1921), Lewis and Randall (1923), Glasstone (1940), and Getman and Daniels 

 (1943) are noteworthy. 



Application of physical principles to the problems of water conduction in trees led 

 to the cohesion theories of Dixon (1914) and Renner (1915). Measurements by 

 MacDougal (1926) have largely substantiated the theoretical considerations involved 

 as have biophysical studies by Bode (1923). 



The general field of plant water relations has been covered by the works of Living- 

 ston (1903),_Maximov (1929a), and Walter (1931fo). Ursprung (1938) has pre- 

 sented a detailed review of most of the early work including his own and that of his 

 collaborators. Ecological aspects of water relations are stressed by Maximov (1929a), 

 Walter (1931&), and Montemaktini (1943). Applications of the principles of soil 



