Section 67. There shall be a board of registration of landscape architects, in this section and in sections sixty-eight and sixty-nine called the board, consisting of five members to be appointed by the governor, citizens of the commonwealth, four of whom shall have been engaged in the practice of landscape architecture for a period of ten years or more prior to their appointment, and shall be registered landscape architects, and one of whom shall be a representative of the public, subject to the provisions of section nine B. As the term of office of a member of the board expires, his successor shall be appointed in like manner for a term of four years. Each member shall continue to serve until the qualification of his successor. The governor may also fill any vacancy in the board for the unexpired portion of the term.