Grafts et al. — 68 — Water in Plants 



rotation of water molecules, inorganic ions, and simple organic molecules, 

 as occurs in simple liquids. Long-chain molecules may be pictured as bend- 

 ing in such regions, globular molecules as turning or shifting. Involved 

 also must be a loosening of the framework to allow structural units to 

 glide by each other, separated by layers of water molecules in which true 

 viscous flow occurs. 



In streaming protoplasm viscous flow can be observed not only along 

 the moving strands but also at the surfaces of plastids, nuclei, vacuoles, 

 and other cellular structures. Such flow must result in the breaking and 

 shifting of many bonds and the activation energy of streaming required to 

 overcome cohesional and lattice forces is presumably derived from cellular 

 oxidations. Frey-Wyssling (1938) proposes that the high content of 

 water in protoplasm may be due not alone to the retention of water by the 

 hydrophilic groups, but to the fact that the meshes produced by the poly- 

 peptide framework are of considerable size, making possible the holding 

 of water and its dissolved salts in these meshes unattached to framework 

 bonds. Such water would be comparatively free and might readily move 

 by replacement. He (1940) attributes decrease in water content, such as 

 occurs during dormancy, to gradual narrowing of the meshes and masking 

 of the hydrophilic groups by polar radicles. Such dehydration would occur 

 gradually without disturbing molecular configuration. 



The views of Lepeschkin (1936, 1938) on the structure of proto- 

 plasm are somewhat different. He proposes that water is not present as 

 a dispersion medium, but that it enters into a loose combination with 

 lipoids and proteins, complexes which comprise the dispersion medium and 

 which he has termed "Vitaids." His theory rests on several lines of evi- 

 dence (a) the relatively rapid movement of lipoid soluble materials through 

 the protoplasm compared to that of water suggesting that water is only one 

 constituent of the dispersion medium and that fats are also a part (b) the 

 typical behavior toward protoplasm of weak acids and other substances, 

 which affect lipoids relatively little. Furthermore, water is believed by 

 Lepeschkin to be absorbed by protoplasm up to a certain point, above which 

 it separates as vacuoles. By placing certain marine foraminifera and algae 

 in dilute sea water he was able to observe vacuolization after limited swell- 

 ing of the organisms. In addition to the water-protein-lipoid dispersion 

 medium, there is postulated to be a variety of dispersed phases, including 

 substances of a hydrophilic, as well as those of a hydrophobic nature. 



M. H. Fischer (1923) advanced similar views of protoplasmic struc- 

 ture on the basis of studies of phenol-water systems: "It is essentially not 

 a solution of protoplasmic material dissolved in water (like phenol-in- 

 water) but one of reverse type, namely, water dissolved in protoplasmic 

 material (like water-in-phenol)." Mason and Phillis (1939) believed 

 that data which they obtained in sap pressing experiments (see later) on 

 cotton leaves seemed to be more in accord with the "Vitaid" hypothesis 

 of Lepeschkin, than with the assumption that water forms the dispersion 

 medium. 



These ideas of Lepeschkin and Fischer have not had widespread 

 acceptance. Brooks and Brooks (1941) reject the viewpoint in question 

 on the basis that "(a) It is improbable that the phenol-water systems are 

 analagous to the other systems mentioned . . . . (b) the abundance and 

 small size of water molecules make it, a priori, improbable that they would 

 be completely separated into separate phases by the large and complex pro- 



