In 2 quart saucepan stir together sugar and corn starch. Gradually stir in water until smooth. Stir in egg yolks. Stirring constantly, bring to boil over medium heat and boil 1 minute. Remove from heat. Stir in lemon juice and margarine. Cool. Turn into pastry shell.
In small bowl with mixer at high speed beat egg whites until foamy. Gradually beat in 1/3 cup of sugar; continue beating until stiff peaks form.
Spread some meringue around edge of filling first. touchig crust all around, then fill center.

HINT: Egg whites CANNOT have any yolk at all. Must be a clean separation of yolk and white. If you had been present the whites will not foam. Bake at 350 degrees F for 15-20 minutes or until lightly browned. Cool.