  We present a model for the spontaneous formation of a striated pattern in
polymerizing microtubule solutions. It describes the buckling of a single
microtubule (MT) bundle within an elastic network formed by other similarly
aligned and buckling bundles and unaligned MTs. Phase contrast and polarization
microscopy studies of the temporal evolution of the pattern imply that the
polymerization of MTs within the bundles creates the driving compressional
force. Using the measured rate of buckling, the established MT force-velocity
curve and the pattern wavelength, we obtain reasonable estimates for the MT
bundle bending rigidity and the elastic constant of the network. The analysis
implies that the bundles buckle as solid rods.
