Liquid crystals can be synthesized but also occur naturally. They represent a state of ordered matter that is intermediate between mobile fluid and stable solid. They can be seen as structures that are a first step away from crystalline regularity (Mackay 1990). Liquid crystals have found a wide range of applications, in fundamental fields as well as in technology. Their potential importance has been acknowledged by the recent Nobel Prize in Physics awarded to P. G. de Gennes for his work in this area (see for example his basic book on the physics of liquid crystals, 1974). Two classes of liquid crystals have been shown to play an important role: (1) the ‘smectics’, which form sheets of mobile molecules perpendicularly oriented to the surface; among these are the amphiphilic molecules (fatty acids) of cytoplasmic microvesicles and cytomembranes; (2) the ‘nematics’, among which are the main variety of ‘cholesterics’, in which the molecules are perpendicular to an axis and in which their orientation rotates continuously and smoothly through a small angle from plane to plane, forming a characteristic chiral arrangement or ‘helicoid’ (the so-called ‘helicoidal pattern’). In the biological field, they are frequently found in the assemblies of long molecules such as DNA (Livolant 1989), and more especially in fibrous composites built of collagen or chitin in animal extracellular matrices (Bouligand 1972; Woodhead-Galloway et at. 1978; Mazur et at. 1989; Giraud-Guille 1992).

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Acta botanica neerlandica

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Koninklijke Nederlandse Botanische Vereniging

J.C. Roland, D. Reis, & B. Vian. (1993). The cholesteric type cell wall: nucleation of defects in the structural order and its relation to spherical cell shape. Acta botanica neerlandica, 42(2), 105–117.