Minn. Stat. § 301.79: EARNED SURPLUS.

The corporation shall set apart as an earned surplus all of its net earnings in each and every year until such earned surplus shall equal the total of the paid-in capital. Said earned surplus shall be held in cash or invested in United States government bonds, and shall be kept and used to meet losses and contingencies of the corporation. Whenever the amount of the earned surplus becomes impaired, it shall be restored to the required amount in the manner provided for its original accumulation.