The commissioner of agriculture shall have supervision over any chemical laboratory established by any cooperative exchange, growers’ exchange, or other business engaged in the harvesting, grading, packing or selling of fruit, for the analyses of fruit for spray residue, and shall cause such firm or individual to register with the department of agriculture. Upon registration and demonstration of ability for the sampling, examination and chemical analyses of fruit for spray residue, such firms or individuals may be permitted to charge fees for the examination of samples of fruit on a basis similar to that charged by the commissioner of agriculture, and report the results of their findings to the owner of such fruit. No certificate attempting to show the presence or amount of arsenic, lead, fluorine, or any other dangerous chemical shall be valid unless issued by authority of the commissioner of agriculture.