A plurality of vertically spaced rows of longitudinally inclined fingers spaced laterally in each row are pivotally supported on transverse horizontal axes near one end. The fingers slope upwardly from the supporting means and also project in the opposite direction from said axes. Vertically movable cam members at the lower ends of the fingers are provided with vertical surfaces that overlie the lower ends of the fingers when the cam members are in their uppermost position. The cam members are m...