Interaction between classes

public partial class Form1 : Form
   {
       static SerialPort _serialPort;

       ....
       }

public partial class Form1 : Form
    {
        static SerialPort _serialPort;

        public Form1()
        {
            InitializeComponent();
        }
        private void ConfigurarToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Config_Serial janela2 = new Config_Serial(this);
            janela2.ShowDialog();
        }

public partial class Config_Serial : Form
    {
        Form1 janela1;
        string[] portas = { "" };




        public Config_Serial(Form1 x)
        {
            InitializeComponent();
            janela1 = x;
            janela1.?  does not appear _serialPort
        }