There shall be a department of law, a department of finance, a department of civil service, a department of purchases and supplies, and such other departments and offices as may be established by ordinance. The commission may discontinue any department or office established by ordinance, and may prescribe, combine, distribute or abolish the functions and duties of departments and offices; but no function or duty assigned by this charter to a particular department or office shall be abolished or assigned to any department or office. No department or office shall be established or discontinued until the recommendation of the city manager thereon shall have been heard by the commission. Departments and offices existing at the time of the adoption of this charter, and not specifically mentioned therein, shall continue as though established thereby until altered or discontinued by ordinance.