A corn harvester has a chassis adapted to travel along the ground and provided on its front with a device for picking ears off cornstalks. A thresher is provided on the chassis for reducing the ears to fragments including pieces of cob, corn kernels, and pieces of husk, and for displacing these fragments backwardly. A floor in the chassis is positioned to receive the fragments from the thresher and has a rear edge provided with a rearwardly extending comb having spaced apart times. The floor and comb are jointly reciprocated to displace the fragments backwardly, during which operation normally the kernels, which are of greater surface density than the other fragments, move to the bottom of the backwardly moving mass. A rotary stripper is provided on the chassis having fingers orbitable between the teeth of the comb. This stripper is rotated at high speed so as to lift most of the husk and cob pieces off the comb and propel them backwardly. This high-speed action separates any kernels that might be stuck to husk and cob pieces therefrom. A riddle is provided behind and below this comb to form therewith a horizontally open gap so that any fragments that fall through the comb land on this riddle. The riddle is also reciprocated so as to move the fragments thereon backwardly with the smaller and denser fragments falling through the riddle. A blower directs a current of air backwardly through the gap and along the riddle to blow the lighter fragments including mainly the husk pieces backwardly. Only the kernels, therefore, pass through the riddle and are caught and collected. Cob pieces too large to fall through the riddle and too dense to be blown away work their way to the rear end of the riddle which they fall off onto the field behind the harvester.