Объединение ячеек в StringGrid

TGridCoord gc;
...
void __fastcall TForm1::StringGrid1MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
gc=StringGrid1->MouseCoord(X,Y);
Rect1 = StringGrid1->CellRect(gc.X, gc.Y);
}
//------------------------------------------------------------------------
void __fastcall TForm1::StringGrid1MouseUp(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
  long Column, Row;
  StringGrid1->MouseToCell(X, Y, Column, Row);
  gc=StringGrid1->MouseCoord(X,Y);
Rect2 = StringGrid1->CellRect(gc.X, gc.Y);
 Caption="caption";
::UnionRect(&Rect, &Rect1, &Rect2);
StringGrid1->Canvas->Brush->Color = StringGrid1->FixedColor;
StringGrid1->Canvas->FillRect(Rect);
Frame3D(StringGrid1->Canvas, Rect, clBtnHighlight, clWindowFrame, 1);
CaptionLength = Caption.Length();
::SetBkMode(StringGrid1->Canvas->Handle, TRANSPARENT );
::DrawText(StringGrid1->Canvas->Handle, Caption.c_str(), CaptionLength, &Rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER );
}