Sec. 3. The salary to be paid monthly upon the order of the School Trustees;  provided, that the salary for the month of September shall not have been paid until the Superintendent of Public Instruction shall have presented a receipt or certificate from the State Superintendent of Public Instruction  showing that he has made all reports required of him;  that the expenses provided for herein shall be paid monthly by the County Treasurer on the order of the Commissioners' Court.