((a)) Each borrower entitled to hold voting stock shall, at the time a loan is made by a bank for cooperatives, own at least one share of voting stock and shall be required by the bank to invest in additional voting stock or nonvoting investment stock at that time, or from time to time, as the lending bank may determine, but the requirement for investment in stock at the time the loan is closed shall not exceed an amount equal to 10 per centum of the face amount of the loan. Such additional ownership requirements may be based on the face amount of the loan, the outstanding loan balance or on a percentage of the interest payable by the borrower during any year or during any quarter thereof, or upon such other basis as the bank determines will provide adequate capital for the operation of the bank and equitable ownership thereof among borrowers.

((b)) Notwithstanding the provisions of subsection (a) of this section, the purchase of stock need not be required with respect to that part of any loan made by a bank for cooperatives which it sells to or makes in participation with financial institutions other than any of the banks for cooperatives. In such cases the distribution of earnings of the bank for cooperatives shall be on the basis of the interest in the loan retained by such bank.