  Using the large hadron calorimeter of the KASCADE experiment, hadronic cores
of extensive air showers have been studied. The hadron lateral and energy
distributions have been investigated in order to study the reliability of the
shower simulation program CORSIKA with respect to particle transport, decays,
treatment of low-energy particles, etc. A good description of the data has been
found at large distances from the shower core for several interaction models.
The inner part of the hadron distribution, on the other hand, reveals
pronounced differences among interaction models. Several hadronic observables
are compared with CORSIKA simulations using the QGSJET, VENUS and SIBYLL
models. QGSJET reproduces the hadronic distributions best. At the highest
energy, in the 10 PeV region, however, none of these models can describe the
experimental data satisfactorily. The expected number of hadrons in a shower is
too large compared to the observed number, when the data are classified
according to the muonic shower size.
