Section 15. Capital stock may be issued for cash, at not less than par, if the shares have par value, and may be issued for property, tangible or intangible, or for services or expenses. Stock issued for cash may be paid for in full before it is issued or by instalments. If it is paid for by instalments, the stock certificate shall be legibly stamped with the words “          per cent paid up, balance payable (stating manner and time of payment)           and shares subject to forfeiture if unpaid,” the facts being truly stated; and, as each instalment is demanded and paid, the certificate shall be stamped accordingly.