  Using the quantum molecular dynamics model, we study the role of mass
asymmetry of colliding nuclei on the fragmentation at the balance energy and on
its mass dependence. The study is done by keeping the total mass of the system
fixed as 40, 80, 160, and 240 and by varying the mass asymmetry of the ($\eta$
= $\frac{A_{T}-A_{P}}{A_{T}+A_{P}}$; where $A_{T}$ and $A_{P}$ are the masses
of the target and projectile, respectively) reaction from 0.1 to 0.7. Our
results clearly indicate a sizeable effect of the mass asymmetry on the
multiplicity of various fragments. The mass asymmetry dependence of various
fragments is found to increase with increase in total system mass (except for
heavy mass fragments). Similar to symmetric reactions, a power law system mass
dependence of various fragment multiplicities is also found to exit for large
asymmetries.
