No corporation shall be organized under the provisions of this subchapter with a capital stock of less than $2,000,000, one-quarter of which must be paid in before the corporation may be authorized to begin business, and the remainder of the capital stock of such corporation shall be paid in installments of at least 10 per centum on the whole amount to which the corporation shall be limited as frequently as one installment at the end of each succeeding two months from the time of the commencement of its business operations until the whole of the capital stock shall be paid in: Provided, however, That whenever $2,000,000 of the capital stock of any corporation is paid in the remainder of the corporation's capital stock or any unpaid part of such remainder may, with the consent of the Board of Governors of the Federal Reserve System and subject to such regulations and conditions as it may prescribe, be paid in upon call from the board of directors; such unpaid subscriptions, however, to be included in the maximum of 10 per centum of the national bank's capital and surplus which a national bank is permitted under the provisions of this Act to hold in stock of corporations engaged in business of the kind described in this subchapter and subchapter I of this chapter. The capital stock of any such corporation may be increased at any time, with the approval of the Board of Governors of the Federal Reserve System, by a vote of two-thirds of its shareholders or by unanimous consent in writing of the shareholders without a meeting and without a formal vote, but any such increase of capital shall be fully paid in within ninety days after such approval; and may be reduced in like manner, provided that in no event shall it be less than $2,000,000. No corporation, except as herein provided, shall during the time it shall continue its operations, withdraw or permit to be withdrawn, either in the form of dividends or otherwise, any portion of its capital. Any national bank may invest in the stock of any corporation organized under this subchapter. The aggregate amount of stock held by any national bank in all corporations engaged in business of the kind described in this subchapter or subchapter I of this chapter shall not exceed an amount equal to 10 percent of the capital and surplus of such bank unless the Board determines that the investment of an additional amount by the bank would not be unsafe or unsound and, in any case, shall not exceed an amount equal to 20 percent of the capital and surplus of such bank.