Water in Plants — ix — Preface 



values of 403 to 745 for some common associated organic liquids ; and a value of 5010 

 for water. The theory that liquids contain points of abnormal coordination (holes) 

 within their structure is receiving continued support and many calculations are being 

 made on the activation energy required for movement of molecules from position to 

 position (flow). Studying thermal conductivity of liquids, Palmer (1948) finds that 

 in associated liquids H-bonds assist in the collisional transfer of heat. This is brought 

 about by (1) causing orientation of the molecules in the direction of flow, and (2) as- 

 sisting transfer by rupture of bonds at the high-temperature end and reforming them 

 at the low-temperature end. If the entropy of vaporization can be considered a measure 

 of H-bonding, then in water 80 per cent of heat transfer is by this mechanism. 



As the picture of water structure becomes clearer, many of the anomalous proper- 

 ties of solutions are being elucidated. Swinging from early assumptions, based on 

 studies of dilute solutions, that all solutions are perfect and that apparent deviations 

 result from association or compound formation, physical chemists went to the other 

 extreme and proposed that all solutes are completely ionized with abnormal behavior 

 resulting from the interaction of force fields (Debye and Huckel). Now a middle 

 course wherein ionic and molecular interaction as well as chemical bonds are given due 

 consideration seems best. With the introduction of spectrum analysis distinctions can 

 be made and the type of bonding identified. Gradually the relations between the 

 thermodynamic properties and the molecular structure of solutions are being studied, 

 and concentrated as well as dilute solutions are being given consideration (Redlich, 

 1949). The literature on the properties of solutions is too large to consider here and 

 the reader is referred to the Journal of Chemical Physics, the Journal of Physical 

 Chemistry and Chemical Reviews as fertile sources. 



Coordination of water is reflected in the high internal pressure or cohesional force 

 which this compound exhibits. Temperley (1947) has shown that liquid water can 

 support tensions up to 60 atmospheres in glass tubes. Using air-free water in Berthelot 

 tubes Scott et a7. (1948) could develop a tension of only 32 atm. Though these values 

 differ appreciably, the latter is sufficient to explain the flow of sap to the tops of the 

 tallest trees. Hydration phenomena have also received attention. For example, Simha 

 and RowEN (1948) conclude that, in systems containing moist cellulose, silk, and wool, 

 behavior at low moisture levels can be explained in terms of adsorption theory ; at 

 high moisture levels the systems can be analysed in terms of a theory of polymer-liquid 

 mixtures ; in between the two extremes a transition occurs. 



Although osmotic pressure measurements continue to serve in the determination 

 of the molecular weight of large molecules, little change has occurred in the theoretical 

 aspects. BuRSTROM (1948) has attempted an evaluation of the significance of turgor 

 of the living cell. Departing from the classical definition "turgor is the pressure acting 

 from inside the cell on the cell wall" (p. 58, last line), Burstrom by devious analysis 

 arrives at the expression T = O — E where T = turgor pressure; O = osmotic 

 value of the cell sap ; and E = osmotic value of the external medium. To us this T 

 is simply a net or corrected osmotic pressure. It is shown as such in Burstrom's Fig. 

 2 (page 61). It could equal our turgor pressure only when the cell is in equilibrium 

 with the external solution of concentration E. As in several previous cases (Crafts, 

 1943), we feel that this redefinition of terms is not justified. It leads to such con- 

 fused statements as — "T increases as the cell loses water — " (page 62, lines 1 and 2), 

 "turgor — expresses a pressure realized in the cell — ," "This deduction of turgor pres- 

 sure — exactly shows the pressure actually exerted from within the cell on the cell 

 wall" (p. 63), and "The turgor pressure must decrease when a cell absorbs water and 

 the wall pressure increases" (p. 64). 



This dilemma seems to arise from a failure to appreciate that (in our symbols) 

 when OP = DPD, T = 0, when OP = TP, DPD = 0, and at all other states OP 

 = DPD + TP. While these relations are most easily examined at equilibrium, a 

 state of flux does not invalidate them. And the definitions which they imply are 

 simple, clear, and in accord with classical considerations of osmotic pressure. 



In the field of cell water relations a number of valuable contributions have ap- 

 peared. In a general discussion of swelling and shrinking (Trans. Faraday Soc, 

 1946) water-holding forces in biological systems received critical consideration. The 

 nature of vacuolation of protoplasm following certain types of swelling is made more 

 clear by Faure-Fremiet. Seifriz presents convincing arguments for a distinction 

 between osmotic pressure and imbibition, and discusses swelling and shrinking phe- 

 nomena in the light of known protoplasmic structure. 



In a subsequent general discussion on interaction of water and porous materials 

 (Faraday Soc. Discussion, 1948), Bennet-Clark restates his belief that water secre- 



