The powers and duties of the trustees shall be vested in and exercised by a body of fifteen (15) trustees. One (1) member of the Board shall be a member of the Maryland House of Delegates. As the terms of the appointed trustees expire, the County Executive shall appoint their successors for a term of four (4) years. In the event that a trustee for any reason fails to serve or to complete any appointment or elected term, the successor shall be appointed by the Executive. The selection of trustees shall be such as to obtain a geographical distribution of trustees throughout the County in so far as practicable and consistent with the purpose of the trust.