The capital stock of each Federal reserve bank shall be divided into shares of $100 each. The outstanding capital stock shall be increased from time to time as member banks increase their capital stock and surplus or as additional banks become members, and may be decreased as member banks reduce their capital stock or surplus or cease to be members. Shares of the capital stock of Federal reserve banks owned by member banks shall not be transferred or hypothecated. When a member bank increases its capital stock or surplus, it shall thereupon subscribe for an additional amount of capital stock of the Federal reserve bank of its district equal to 6 per centum of the said increase, one-half of said subscription to be paid in the manner hereinbefore provided for original subscription, and one-half subject to call of the Board of Governors of the Federal Reserve System. A bank applying for stock in a Federal reserve bank at any time after the organization thereof must subscribe for an amount of the capital stock of the Federal reserve bank equal to 6 per centum of the paid-up capital stock and surplus of said applicant bank, paying therefor its par value plus one-half of 1 per centum a month from the period of the last dividend. When a member bank reduces its capital stock or surplus it shall surrender a proportionate amount of its holdings in the capital stock of said Federal Reserve bank. Any member bank which holds capital stock of a Federal Reserve bank in excess of the amount required on the basis of 6 per centum of its paid-up capital stock and surplus shall surrender such excess stock. When a member bank voluntarily liquidates it shall surrender all of its holdings of the capital stock of said Federal Reserve bank and be released from its stock subscription not previously called. In any such case the shares surrendered shall be canceled and the member bank shall receive in payment therefor, under regulations to be prescribed by the Board of Governors of the Federal Reserve System, a sum equal to its cash-paid subscriptions on the shares surrendered and one-half of 1 per centum a month from the period of the last dividend not to exceed the book value thereof, less any liability of such member bank to the Federal Reserve bank.