Section 3. Each of said executive offices shall be headed by a secretary, who shall be appointed by and serve at the pleasure of the governor. The secretary shall receive such salary as the governor may determine, and shall devote his full time to the duties of his office. Each secretary may, notwithstanding section 45 of chapter 30 and chapter 31, subject to the approval of the governor and subject to appropriation, appoint 1 or more undersecretaries for the executive office, each of whom shall serve at the pleasure of her appointing secretary. Each person appointed as an undersecretary shall have experience and shall know the field or functions of such position, shall receive such salary as the secretary shall determine, subject to the approval of the governor, and shall devote his full time to the duties of the office.