  We prove that the (real or complex) chromatic roots of a series-parallel
graph with maxmaxflow Lambda lie in the disc |q-1| < (Lambda-1)/log 2. More
generally, the same bound holds for the (real or complex) roots of the
multivariate Tutte polynomial when the edge weights lie in the "real
antiferromagnetic regime" -1 \le v_e \le 0. This result is within a factor
1/log 2 \approx 1.442695 of being sharp
