could not assigne member class

private void FormLoad(object sender, EventArgs e)
{
    MyPlate mp = new MyPlate();
    mp.LP[0].P.X = 1;<-----------Error
}

class point
{
private double x, y, z;
public point() { }
public point(double xi, double yi, double zi)
{ X = xi; Y = yi; Z = zi; }
public double X { get { return x; } set { x = value; } }
public double Y { get { return y; } set { y = value; } }
public double Z { get { return z; } set { z = value; } }
}
//---------------------------------------------
class MyLine
{
private point[] p = new point[100];
public MyLine() { }
public MyLine(point[] Xp)
{
    p = Xp;
    allocate();
}
private void allocate()
{int i;
    for(i = 0; i < 100; i++)
    P[i] = new point();
    //p[i] = new point();
}
public point[] P{ get { return p; } set { p = value; } }
}
//-----------------------------------------------------
class MyPlate
{
private MyLine[] lp = new MyLine[100];
private point[]    p = new point[100];
public MyPlate() { }
public MyPlate(MyLine[] Xlp,  point[] Xp) 
{
    LP = Xlp;
    P  = Xp;
    allocate();
}
private void allocate()
{int i;
    for(i=0;i<100;i++)
    {
        LP[i]=new MyLine();
        P[i] = new point();
        //lp[i] = new MyLine();
        //p[i] = new point();
    }
}
//---------------------------------------------------
public MyLine[] LP { get { return lp; } set { lp = value; } }
public point[] P { get { return p; } set { p = value; } }
}