Ge1-xSix (x less than or equal to 10 at%) single crystals were grown with the float zone technique using a monoellipsoid mirror furnace. The feed rod consisted of pre-synthesized Ge0.95Si0.05 polycrystalline material with an initial composition of pure germanium. Several boron-doped (1-2 x 10(17) at cm (-3)) crystals were grown using (1 0 0) Ge seeds. Taking advantage of the pre-synthesized feed rods, a defined macrosegregation could be achieved in the grown crystals with a linear slope at the beginning (approximate to 0.5 at% mm (-1)) followed by a plateau region with a constant silicon distribution (Si concentration up to 10 at%, fluctuation rate: less than or equal to +/-0.3 at%). The etch pit density was in the range of 7 x 10(3)-2 x 10(4)cm(-2) Micrographs of the etched crystals show sharp changes in interface curvature at the crystal edges. These distortions of the interface morphology are a direct function of the Si concentration; they are considered to be caused by solutal Marangoni convection. Theoretical considerations show that the flow direction and strength vary significantly from a solutal Marangoni convection regime directly in front of the solid-liquid interface to a thermal Marangoni convection regime within the bulk melt.