  On the basis of the thermodynamic theory of the excluded volume effects, we
show that the size exponent varies abruptly, depending on the change of the
segment concentration. For linear polymers, the exponent changes
discontinuously from $\nu=3/5$ for the isolated system ($\bar{\phi}=0$) in good
solvents to $\nu=1/2$ in the finite concentration ($0<\bar{\phi}\le1$), while
for branched polymers having $\nu_{0}=1/4$, the corresponding exponent varies
from $\nu=1/2$ ($\bar{\phi}=0$) to $\nu\cong 1/3$ ($0<\bar{\phi}\le1$).
