  Wilson loops in the adjoint representation are evaluated on cooled lattices
in SU(2) lattice gauge theory. It is found that the string tension of an
adjoint Wilson loop vanishes, if the loop is evaluated in a sub-ensemble of
configurations in which no center vortex links the loop. This result supports
our recent proposal that the adjoint string tension, in the Casimir-scaling
regime, can be attributed to a center vortex mechanism.
