  The scaling of the shear modulus near the gelation/vulcanization transition
is explored heuristically and analytically. It is found that in a dense melt
the effective chains of the infinite cluster have sizes that scale sub-linearly
with their contour length. Consequently, each contributes k_B T to the
rigidity, which leads to a shear modulus exponent d\nu. In contrast, in phantom
elastic networks the scaling is linear in the contour length, yielding an
exponent identical to that of the random resistor network conductivity, as
predicted by de Gennes'. For non-dense systems, the exponent should cross over
to d\nu when the percolation length becomes much larger than the
density-fluctuation length.
