  Recently Alan Sokal studied the leading root $x_0(q)$ of the partial theta
function $\Theta_0(x,q)=\sum\limits_{n=0}^\infty x^nq^{\binom n2}$, considered
as a formal power series. He proved that all the coefficients of
$$-x_0(q)=1+q+2q^2+4q^3+9q^4+...$$ are positive integers. I give here an
explicit combinatorial interpretation of these coefficients. More precisely, I
show that $-x_0(q)$ enumerates rooted trees that are enriched by certain
polyominoes, weighted according to their total area.
