(a) After January 1, 1950, any person who becomes an employee of any employer which operates under a merit system of personnel administration and which is covered by the retirement system shall become a member of the retirement system as a condition of his employment, except as otherwise specifically excluded.

(b) Any person who was an employee during the fiscal year ending June 30, 1949, or who becomes an employee prior to January 1, 1950, shall become a member unless prior to January 1, 1950, he files with the board of trustees, on a form provided by it, a notice of his election not to be included in the membership of the retirement system, together with a duly executed waiver of all present and prospective benefits which would otherwise accrue to him by participating in the retirement system. Such an employee may thereafter apply for and be admitted to membership, but without credit for service rendered after July 1, 1949, and prior to the time he becomes a member and without prior service credit, unless he pays into the retirement system the amount of deductible contributions that would have been paid by such member together with interest on such amount equal to the amount of interest earned by the retirement system at 3 1/2 percent per annum had the amounts been paid in during the period. Upon making such payments, he shall be entitled to all service credits from the year 1949.

(c) The membership of any person shall terminate if he retires under this retirement system, withdraws his contributions, or renders less than one year of service within a period of five consecutive years as a member. No benefit under the retirement system shall accrue to a member's account while he is not in service as an employee and no contribution shall be made to the retirement system by the member, the state, or any other employer during any such time.

(d) The board of trustees may continue the membership of any person while such person is on leave of absence with stipend for professional training when such leave is approved in writing by the employer for which the employee renders service, provided that a member who receives a stipend while on leave for professional training shall make a monthly contribution to the retirement system, which contribution shall be the same basic percentage of his salary as an employee as he contributed in the last month prior to the effective date of leave. A member shall be considered as being in service while on such leave.