Signals of quark substructure in hadron reactions at intermediate energies

Exotic hadrons of a few GeV/c^2 mass, exhibiting a spectrum determined by the perturbative interaction of a non-minimal number of valence quarks, have long been predicted as signals of the underlying QCD structure. Models that include the confinement region, in addition to the region of asymptotic freedom, predict exotic masses 0.2--0.8 GeV higher than the others. The R-matrix hybrid model has made the most detailed predictions, some of which have been experimentally observed. Here we will give an introduction to the model and review the status of its predictions and new applications.