Section 17A. Upon the filing of a petition with the chairman of the state committee of a political party, signed by fifty enrolled members of such party within a senatorial district, such chairman shall call a convention of all the ward and town committees in said senatorial district for the purpose of endorsing candidates from among the enrolled members of the party for nomination for election to membership on the state committee from said senatorial district.

Said convention shall be held not later than the tenth day prior to the time provided for the filing of nomination papers for said membership, and shall be held in the ward or town within the senatorial district which cast the highest vote at the preceding biennial state election for the political party candidate for governor.

Said convention shall elect from among its members a chairman and a secretary and shall make suitable rules for the conduct of its business. Each ward and town committee represented at such convention shall be entitled to one vote and one additional vote for every fifteen hundred votes or major fraction thereof above the first fifteen hundred votes cast at the preceding biennial state election in such ward or town for the political party candidate for governor.

Every certificate of nomination of a candidate endorsed for nomination by such a convention shall state that the nominee has been endorsed by such convention, and shall include such facts as are required by section eight. Such certificate shall be signed, sworn to and filed with the state secretary as required by section five.

Each candidate endorsed by such a convention shall not later than the last day and hour for filing nomination papers for said membership file with the state secretary his written acceptance of the nomination, otherwise his name shall not be printed on the ballot as a candidate for member of the state committee for which he was nominated. Such candidate may not withdraw such acceptance.