Section 80. Income debentures

With the approval of the commissioner the
  certificate, or an amended certificate, may authorize  the  issuance  of
  income  debenture  certificates bearing no greater interest than six per
  centum per annum. In the case  of  a  housing  company  organized  as  a
  corporation the directors thereof may, with the consent of two-thirds of
  the holders of the preferred shares issued and outstanding, offer to the
  shareholders  of  the housing company, the privilege of exchanging their
  shares in such quantities and at such times as may be  approved  by  the
  commissioner  for  such income debenture certificates. In no event shall
  the amount of shares of the housing company be less than ten per  centum
  of the total of shares and income debentures.