How to Serialize and DeSerialize List Lines?

    [Serializable()]
    public class ObjectToSerialize : ISerializable
    {
        private List<Line> xLines;
        private List<Line> yLines;
        public List<Line> XLines
        {
            get { return this.xLines; }
            set { this.xLines = value; }
        }
        public List<Line> Xlines
        {
            get { return this.xLines; }
            set { this.xLines = value; }
        }

        public ObjectToSerialize()
        {
        }

        public ObjectToSerialize(SerializationInfo info, StreamingContext ctxt)
        {
            try
            {
                this.xLines = (List<Line>)info.GetValue("xLines", typeof(List<Line>));
                          }
            catch(Exception e)
            {
                System.Windows.Application.Current.Resources["infoSB"] = e.Message;
            }
        }

        public void GetObjectData(SerializationInfo info, StreamingContext ctxt)
        {
            info.AddValue("xLines", this.xLines);
            //info.AddValue("xLinesObj", this.obj);
        }
    }

    public class Serializer
    {
        public Serializer()
        {
        }

        public void SerializeObject(string filename, ObjectToSerialize objectToSerialize)
        {
            using (Stream stream = File.Open(filename, FileMode.Create))
            {
                BinaryFormatter bFormatter = new BinaryFormatter();
                bFormatter.Serialize(stream, objectToSerialize); //Here I get the exception
                stream.Close();
            }
        }

        public ObjectToSerialize DeSerializeObject(string filename)
        {

            ObjectToSerialize objectToSerialize = null;
            try
            {
                using (Stream stream = File.Open(filename, FileMode.Open))
                {
                    BinaryFormatter bFormatter = new BinaryFormatter();
                    objectToSerialize = (ObjectToSerialize)bFormatter.Deserialize(stream);
                    stream.Close();
                }
            }
            catch (Exception e)
            {
                System.Windows.MessageBox.Show(e.Message);
            }
            return objectToSerialize;

        }
    }

              ObjectToSerialize objectToserialize = new ObjectToSerialize();
              objectToserialize.Xlines = xLines; //List<Line> xLines
              Serializer serializer = new Serializer();
              serializer.SerializeObject(serializeFileName, objectToserialize);

How can I make Line as Serializable?