When the board shall decide that it is to the best interest of the district that the duties in this code designated to be performed by the treasurer should be done and performed by the secretary of such district, they may at their option, by resolution, duly presented and approved by such board assign such duties to the secretary of such district; provided, that the duty of receiving any funds collected by the secretary and the depositing and disbursing of such funds by order of the board shall always be and remain the duty and responsibility of the treasurer. The board shall, in said resolution, devise a proper system or plan whereby the secretary may pay to the treasurer all moneys collected by him and take receipts therefor.