The property GridStyle determines the type of the grid:
gsNone
No grid is displayed
gsPoints
The grid is indicated by points
gsVertLines
Vertical grid lines
gsHorizLines
Horizontal grid lines
gsLines
Both vertical and horizontal grid lines
gsHorizDotLines
Only horizontal, dotted grid lines will be displayed
gsVertDotLines
Only vertical, dotted grid lines will be displayed
gsDotLines
Both vertical and horizontal grid lines are displayed as dotted lines.
Hint:
Grid lines are rather costly as far as processing time is concerned. Thus you should be careful to avoid too many grid lines if rendering speed is of any essence.