Section 29. A company, unless expressly authorized by its charter or by special law, shall not issue bonds, coupon notes or other evidences of indebtedness payable at periods of more than one year after their date to an amount which, including the amount of all such securities previously issued and outstanding, computed as provided in section fifty-three of chapter one hundred and fifty-nine, exceeds in the whole the amount of its capital stock at the time actually paid in; but this limitation shall not apply to an issue of bonds for the purpose of paying and refunding at maturity bonds lawfully issued prior to June second, eighteen hundred and ninety-seven; nor shall it apply to such of the bonds issued or to be issued under a mortgage as are deposited to retire at or before maturity bonds or other evidences of indebtedness previously issued and outstanding at the date of such mortgage, and as do not exceed the par value of the funded or other debt so to be retired; nor shall it apply to bonds, coupon notes or other evidences of indebtedness payable at periods of more than one year after their date, in addition to, and not exceeding twenty per cent of, the amount so computed, which shall be authorized as consistent with the public interest by the department, and which shall be subject to such requirement as to a sinking fund or other method of retiring said evidences of indebtedness within a period not exceeding ten years, as the department may prescribe, to provide means for, or to fund, the actual cost of replacement or reconstruction of any existing property; and such company shall not issue the securities specified in this section unless authorized by a vote of its stockholders at a meeting called therefor.