Section 20. Departments limited. All executive and administrative officers, agencies, and instrumentalities of the executive department of the state and their respective functions, powers, and duties, except for the office of governor, lieutenant governor, secretary of state, state controller, state treasurer, attorney general and superintendent of public instruction, shall be allocated by law among and within not more than twenty departments by no later than January 1, 1975. Subsequently, all new powers or functions shall be assigned to departments, divisions, sections or units in such a manner as will tend to provide an orderly arrangement in the administrative organization of state government. Temporary agencies may be established by law and need not be allocated within a department; however, such temporary agencies may not exist for longer than two years.