A crop cutting device including knives pivotally mounted below a crop guiding surface. Each knife is pivotable between a retracted position in which it is located below the guiding surface and an extended position. At least a cutting edge of the knife projects above the surface. A selector mechanism selectively holds spring loaded parts of operating members to maintain the corresponding knife in its retracted inoperative position while the operating member is moved to its second position. The selector mechanism includes a shaft carrying a plurality of cam elements which are mounted on the shaft and arranged to be moved to a position for blocking a respective spring loaded part upon rotation of the shaft from a non-holding to a holding position.