The Secretary of Agriculture is authorized, at such times as he deems appropriate, to convey by appropriate conveyances, without consideration, the interest of the United States in the lands, including water rights, buildings, and improvements presently comprising or appurtenant to the following dry land and irrigation field stations, to the States in which such stations are located, when, in the opinion of the Secretary of Agriculture, the transfer of any such station will result in establishing a more effective program in the cooperative agricultural experimental work of the Department of Agriculture and the respective State and the furtherance of agricultural experimental work on a national or regional basis will be better served by such transfer: Huntley, Montana; Mitchell, Nebraska; Fallon, Nevada; Tucumcari, New Mexico; Hermiston, Oregon; Sheridan, Wyoming: Provided, That when any or all of the land, including water rights, comprising any such station is public-domain land, only the Secretary of the Interior may by patent or other appropriate conveyance transfer such lands to the respective States: Provided further, That when any easement necessary to a station conveyed or patented hereunder is on public-domain lands, only the Secretary of the Interior may grant such easements to the State to which the station has been conveyed.