Combination in apparatus for producing rod-shaped members of crystalline material includes a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in the receptacle substantially along the vertical central axis of the receptacle for supporting a rodshaped member of crystalline material therebetween, heating means mounted in the receptacle for producing a melting zone in the rod-shaped crystalline member, the heating means and the holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, and drive means extending into the receptacle through a wall portion other than the bottom wall portion from a location outside the receptacle for moving the holders and the heating means relative to one another.