dt = 0.5; dx = 0.25;
[t,x] = meshgrid( 0:dt:10, 0:dx:2);
S = x.*(1-x); L = sqrt(1+S.^2);
quiver( t, x, 1./L, S./L, 0.3 );
axis auto tight
title('x'' = x(1-x) Dir. Field') 