3307.  Premiums and discount bonds.--Where any part of the principal consists of bonds or other obligations for the payment of money, they shall be deemed principal at their inventory value or in default thereof at their market value at the time the principal was established, or at their cost where purchased later, regardless of their par or maturity value; and upon their respective maturities or upon their sale, any loss or gain realized thereon shall fall upon or enure to the principal.