| Abstract: | The internodal cells of the alga Nitella opaca L, which arein the form of long thin cylinders, exhibit the phenomenon ofspiral growth, i.e. as the cells elongate they also twist abouttheir longitudinal axis. It has been shown in an earlier paper(Probine and Preston, 1962) that the cell wall is mechanicallyanisotropic. In this paper the moduli necessary to describethe elastic behaviour of a material possessing this sort ofsymmetry are considered. It is pointed out that if the Nitellacell is regarded as a thin-walled cylinder built of a materialpossessing orthorhombic elastic symmetry, then there can bea coupling between shear and extension which will produce atorsional twist as the cylinder is pressurized. It is suggested that this is the basic mechanism of spiral growth.Experimental evidence is presented which supports this view. |
