The executive department shall consist of all state elective and appointive officials and employees except officials and employees of the legislative and judicial departments. In addition to the governor and lieutenant governor there shall be a state auditor, secretary of state, attorney general, a state treasurer, an office of administration, a department of agriculture, a department of conservation, a department of natural resources, a department of elementary and secondary education, a department of higher education, a department of highways and transportation, a department of insurance, a department of labor and industrial relations, a department of economic development, a department of public safety, a department of revenue, a department of social services, a department of the National Guard, and a department of mental health. In addition to the elected officers, there shall not be more than sixteen departments and the office of administration. The general assembly may create by law two departments, in addition to those named, provided that the departments shall be headed by a director or commission appointed by the governor on the advice and consent of the senate. The director or commission shall have administrative responsibility and authority for the department created by law. Unless discontinued all present or future boards, bureaus, commissions and other agencies of the state exercising administrative or executive authority shall be assigned by law or by the governor as provided by law to the office of administration or to one of the sixteen administrative departments to which their respective powers and duties are germane.