The power to propose the revision or amendment of any portion or portions of this constitution by initiative is reserved to the people, provided that, any such revision or amendment, except for those limiting the power of government to raise revenue, shall embrace but one subject and matter directly connected therewith to the structure of state government and taxation. It may be invoked by filing with the custodian of state records a petition containing a copy of the proposed revision or amendment, signed by a number of electors in each of one half of the congressional districts of the state, and of the state as a whole, equal to eight percent of the votes cast in each of such districts respectively and in the state as a whole in the last preceding election in which presidential electors were chosen.