Within the extreme diversity of aquatic and terrestrial plant genera, each has characteristic cell wall forms. A number of hypotheses have been advanced to explain differences in microfibril arrangements across anyone such wall. Of those, only the 'multinet' theory, which involves the postulation of reorientation of microfibrils caused by cell extension, now has a substantial number of ad herents. However, many scientists are sceptical of its validity; obviously it is incompatible with various observed microfibril arrangements. The tenet of this study is that any such hypothesis can be valid only if it is applicable to all plant forms and wall types. Initially, reanalyses are made of data claimed to confirm justification for multi net postulations. The results show that previous deductions from those data, in support of multinet, are subject to serious challenge. Similarly, a re-examination of the observations, which inspired the multinet theory, shows they have a more logical explanation. Herein, it is concluded that cell wall development involves biophysical factors, which neces sarily prevent multinet's postulated large reorientations of microfibrils, after their formation. Unfortunately the previously most recent published theory, which is based on the absence of reorientation during extension, fails to answer the fundamental question of how alternating orientations between lamellae are controlled, or explain variations in thickness of wall layers. Extensive published data are used to identify forces involved in cell wall development.

The series on 'Charged and Reactive Polymers' was set forth in two volumes concern ing the fundamentals and applications of polyelectrolytes. A follow-up on 'Charged Gels and Membranes' would therefore seem appropriate, necessitating, however, some explanation for non-specialists. Theories of the most dilute gels originate in that of concentrated polyelectrolytes: the methods and problems are similar in structural, spectroscopic or thermodynamic properties. The borderline can be situated in dialysis conducted with a 'bag' imper meable to polyelectrolytes but not to small ions, solutes and water. One may recall Donnan's use of such a system to experiment and discover his famous law of unequal distribution of ions of different charge inside and out. Remark ably so, it is the difference in scale which characterizes the difference between poly electrolyte solutions and gels and membranes: the colloidal solution of macro molecules is heterogeneous only on the microscopic level, whereas the gel-solution system is a macroscopically heterogeneous one. A gel is formed when weak or strong cohesive forces counterbalance the dispersing ones (usually by crosslinking) without inhibiting the penetration of solvent and of small solutes into the polymeric network. The solvophile macromolecules cannot invade the total volume of liquid. As a result of phase-segregation excess solution and gel coexist and interact. The macroscopic swelling depends on gel cross-linking as well as on ionic concentration and type and ion-selectivities are observed."