  Glueballs and hybrids are predicted to exist but searches for them have
failed to provide conclusive evidence. One--gluon exchange is not an important
part of strong interactions in this energy regime. Instead, quarks seem to
interact indirectly, via changes of the QCD vacuum. Strong interactions seem to
be governed by instanton--induced interactions; the chiral soliton model gives
a more suitable interpretation of the $\Theta^+(1540)$ than models based on the
dynamics of four quarks and one antiquark.
