unit Unit2;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

type
  TForm2 = class(TForm)
  private
    {Private declarations}
  public
    {Public declarations}
    constructor CreateWithCaption(aOwner: TComponent; aCaption: string);
end;

var
  Form2: TForm2;

implementation

{$R *.DFM}

constructor TForm2.CreateWithCaption(aOwner: TComponent; aCaption: string);
begin
  Create(aOwner);
  Caption := aCaption;
end;

uses
 Unit2;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Unit2.Form2 :=Unit2.TForm2.CreateWithCaption(Application, 'My Caption');
  Unit2.Form2.Show;
end;