Whenever the Secretary of Agriculture deems that the delegation of the whole or any part of any regulatory function which the Secretary is, now or after April 4, 1940, required or authorized to perform will result in the more expeditious discharge of the duties of the Department of Agriculture, he is authorized to make such delegation to any officer or employee designated under this section. The Secretary is authorized to designate officers or employees of the Department to whom functions may be delegated under this section and to assign appropriate titles to such officers or employees. There shall not be in the Department at any one time more than two officers or employees designated under this section and vested with a regulatory function or part thereof delegated under this section. The Secretary may at any time revoke the whole or any part of a delegation or designation made by him under this section.