C# Form Height implement Scroll Bar

public class Form1 : Form
    { 
        private System.ComponentModel.IContainer components = null;
        private System.Windows.Forms.Panel panel1;
        private string _dir = @"C:\img";
        private string _pat = "*.bmp";
        public Form1()
        {
            InitializeComponent();
            LoadPictureBoxes();
        }
        private void LoadPictureBoxes()
        {
            int count = 0;
            foreach(string path in Directory.GetFiles(_dir,_pat))
            {            
                PictureBox pb = new PictureBox();
                pb.Image = new Bitmap(path);
                pb.Height = 100;
                pb.Width = panel1.Width - 5;
                pb.Left = 0;
                pb.Top = count * 100;
                panel1.Controls.Add(pb);
                count++;
            }
        }
        private void InitializeComponent()
        {
            this.panel1 = new System.Windows.Forms.Panel();
            this.SuspendLayout();
            // 
            // panel1
            // 
            this.panel1.Dock = System.Windows.Forms.DockStyle.Fill;
            this.panel1.Location = new System.Drawing.Point(0, 0);
            this.panel1.Name = "panel1";
            this.panel1.Size = new System.Drawing.Size(505, 659);
            this.panel1.TabIndex = 0;
            this.panel1.VerticalScroll.Enabled = true;
            this.panel1.AutoScroll = true;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(505, 659);
            this.Controls.Add(this.panel1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }
    }