  We observed reduction of multiple Coulomb scattering of 855 MeV electrons
within a Si crystalline plate w.r.t. an amorphous plate with the same mass
thickness. The reduction owed to complete or partial suppression of the
coherent part of multiple scattering in a crystal vs crystal orientation with
the beam. Experimental data were collected at Mainz Mikrotron and critically
compared to theoretical predictions and Monte Carlo simulations. Our results
highlighted maximal 7 % reduction of the r.m.s. scattering angle at certain
beam alignment with the [100] crystal axes. However, partial reduction was
recorded over a wide range of alignment of the electron beam with the crystal
up to 15 deg. This evidence may be relevant to refine the modelling of multiple
scattering in crystals for currently used software, which is interesting for
detectors in nuclear, medical, high energy physics.
