All moneys collected from such levy shall be expended exclusively to effectuate the purposes and objects of this chapter. They shall be generally expended on promotion and improvement of the various commodities approximately in the ratio that funds are derived from such commodities, after deducting suitable amounts for general overhead and basic general research, unless a majority of the functioning state commodity committees consent to a larger expenditure on behalf of any commodity or commodities. Any funds contributed to the commission by any special group or raised by an additional levy on any commodity or classification thereof, shall be expended only in connection with such commodity.