Half of the seed potatoes that are planted each spring are infected with some plant disease. Black leg, Black scurf, Common scab, and Dry rots are the commonest of these diseases. They cut down the stand, injure the roots, mar the potatoes and reduce the yield. Illustration on cover shows the seed potatoes from a 2 1/2 bushel sack bought in the open market, sorted into two lots: those free from disease and those not free. Note that there are more diseased potatoes than healthy ones. '!'his is not an unusual case; in fact, it is somewhat better than the average. Such potatoes can be made into good seed by treating them, but seed treatment will not make good seed out of culls. The little potatoes and those badly diseased should be discarded for seed purposes.