The people reserve to themselves the power to propose laws and to enact and reject laws, called the initiative, and the power to approve or reject laws enacted by the legislature, called the referendum. The power of initiative extends only to laws which the legislature may enact under this constitution. The power of referendum does not extend to acts making appropriations for state institutions or to meet deficiencies in state funds and must be invoked in the manner prescribed by law within 90 days following the final adjournment of the legislative session at which the law was enacted. To invoke the initiative or referendum, petitions signed by a number of registered electors, not less than eight percent for initiative and five percent for referendum of the total vote cast for all candidates for governor at the last preceding general election at which a governor was elected shall be required.