The ornamental design for a portion of a tractor, as shown and described.
FIG. 1 is a front view of a portion of a tractor showing my new design. The part of the photograph shown in coarse dot pattern and outlined in dashed lines illustrates a portion of the tractor that forms no part of the claimed design;
FIG. 2 is a left side view thereof. The part of the photograph shown in coarse dot pattern and outlined in dashed lines illustrates a portion of the tractor that forms no part of the claimed design;
FIG. 3 is a right side view thereof. The part of the photograph shown in coarse dot pattern and outlined in dashed lines illustrates a portion of the tractor that forms no part of the claimed design;
FIG. 4 is a top plan view thereof. The part of the photograph shown in coarse dot pattern and outlined in dashed lines illustrates a portion of the tractor that forms no part of the claimed design.
FIG. 5 is a right front perspective view thereof. The part of the photograph shown in coarse dot pattern and outlined in dashed lines illustrates a portion of the tractor that forms no part of the claimed design. The left front perspective view of the claimed design, although not illustrated, is a mirror image of the right front perspective view shown in FIG. 5; and,
FIG. 6 is a left front perspective view thereof. The parts of the photograph shown in coarse dot pattern and outlined in dashed lines illustrate portions of the tractor that form no part of the claimed design.