  Collective flow of protons and negative pions has been studied within the
momentum region of $4.2 \div 4.5$ AGeV/c ($E =3.4 \div 3.7$ AGeV) for different
projectile-target combinations involving carbon and, specifically, He-C, C-C,
C-Ne, C-Cu and C-Ta. The data stem from the SKM-200-GIBS streamer chamber and
from Propane Bubble Chamber systems utilized at JINR. The directed flow of
protons grows dramatically in the carbon region when the counterpart nucleus
grows in mass between He and Ta. The elliptic proton flow points out of the
reaction plane and also strengthens as system mass increases. Within the
reaction plane, the negative pions flow in the same direction as protons for
the lighter of the investigated systems, He-C, C-C and C-Ne, and in the
opposite direction for the heavier, C-Cu and C-Ta. The Quark-Gluon String Model
reproduces observed changes in the flow with system mass.
