Section 18. Every corporation may issue preferred stock of one or more classes to an amount not exceeding at any time the amount of the common stock then outstanding and all cash premiums paid to the company thereon and applied to the purposes of the corporation with such preferences and voting powers or restrictions or qualifications thereof as shall be fixed and determined in the agreement of association at the organization of the corporation; or after organization, as to any such preferred stock or additional class thereof, by a two thirds vote of all the stock entitled to vote thereon or by a by-law adopted by a two thirds vote of all the stock entitled to vote thereon, at a meeting duly called for the purpose. This section shall not apply to corporations organized under chapter one hundred and fifty-six or to railroad corporations or street railway companies.