Fig. 7. Spatial dynamics of the rosettes depends on substrate rigidity. Simultaneous evolution with time of the expansion/contraction rate E (blue curve) and of the rotation rate (grey curve). (B) Simultaneous evolution of the orthogonal shear rate S₁ (green curve) and of the oblique shear rate S₂ (grey curve). (C) Velocity field superimposed to the rosette image at time t=120 seconds, which corresponds to the maximum expansion rate (1); (D) Velocity field superimposed to the rosette image at time t=255 seconds which corresponds to the maximum contraction rate (2). This rosette was observed on a rigid substratum (glass). (E) Mean rate of expansion and contraction averaged over several rosettes and for each value of substrate rigidity computed by n=8 for 0.08% gel; n=7 for 0.2% gel; and n=16 for glass. Data are expressed as mean ± s.d.