Undo operation for series in chart

I want to restore previous series after changing some Yvalues[0] multiple times in the chart. So I have implemented undo operation using memento pattern.

But it's not working and there is no error while running. Below is the originator, memento and caretaker.

public class Originator
{

    private Series _series = new Series();

    public Originator(Series series)
    {
        _series = series;
    }
    public Series OSeries
    {
        get
        {
            return _series;
        }
        set
        {
            _series = value;
        }
    }

    public Memento SaveSeries()
    {
        return new Memento(_series);
    }

    public void RestoreSeries(Memento m)
    {
        this._series = m.MMseries;
    }
 }

public class Memento
{
    private Series _series =new Series();

    public Memento(Originator org)
    {
        this._series = org.OSeries;
    }
    public Memento(Series mseries)
    {
        _series = mseries;
    }

    public Series MMseries
    {
        get
        {
            return _series;
        }
        set
        {
            _series = value;
        }
    }
}
public class Caretaker
{
    //  private static Caretaker _instance;


    //  public Caretaker() { }

    private Memento chartMemento;
    public Memento Memento
    {
        get
        { return chartMemento; }

        set
        {  chartMemento = value; }

    }
}

Created objects in public partial class Form1 : Form

Originator _org;
Caretaker taker = new Caretaker();

While loading the chart from a file, open_file function contains this code:

_org = new Originator(global_series); //For undo/redo operation
while (chart1.Series.Count > 0) { chart1.Series.RemoveAt(0); }

chart1.Series.Add(global_series);
taker.Memento = _org.SaveSeries();

For Undo_button:

_org.RestoreSeries(taker.Memento);
while (chart1.Series.Count > 0) { chart1.Series.RemoveAt(0); }
global_series = _org.OSeries;
chart1.Series.Add(global_series);