A subscription for shares of a corporation to be organized shall be irrevocable for a period of six months, unless otherwise provided by the terms of the subscription agreement or unless all of the subscribers consent to the revocation of the subscription. Unless otherwise provided in the subscription agreement, subscriptions for shares, whether made before or after the organization of a corporation, shall be paid in full at such time, or in such installments and at such times, as determined by the board of directors. Any call made by the board of directors for payment on subscriptions shall be uniform as to all shares of the same class or as to all shares of the same series, as the case may be. In case of default in the payment of any installment or call when the payment is due, the corporation may proceed to collect the amount due in the same manner as any debt due the corporation. The bylaws may prescribe other penalties for failure to pay installments or calls that may become due, but no penalty working a forfeiture of a subscription, or of the amounts paid thereon, shall be declared as against any subscriber unless the amount due thereon remains unpaid for a period of thirty days after written demand has been made therefor. If mailed, the written demand shall be deemed to be made when deposited in the United States mail in a sealed envelope addressed to the subscriber at his last post-office address known to the corporation, with postage thereon prepaid. In the event of the sale of any shares by reason of any forfeiture, the excess of proceeds realized over the amount due and unpaid on the shares shall be paid to the delinquent subscriber or to his legal representative.