Fig. 6. (A) Behaviour of microtubules on thinner (Thin) and thicker (Thick) bundles at various concentrations of Ca²⁺. The microtubules that attached to the bundles showed sliding movement (solid boxes), back-and-forth movement (hatched boxes) or no movement (open boxes). The numbers of bundles with which microtubules interacted are shown in the right-hand column. (B) The ratio of the number of occurrences of microtubule sliding on the thinner bundles to that on the thicker bundles at various concentrations of Ca²⁺.