Workers on Virus Diseases of the Potato labour under a disadvantage inasmuch as they are frequently confronted with the difficulty of obtaining positive results of infection in one and the same season. Moreover, tubers resulting from a plant which has been artificially infected in one season, retain the secret of the success or otherwise of the operation until adult plants have been grown from them in the succeeding year. Any method which will sensibly curtail this long waiting period is welcome. As long ago as 1788, Joseph Webb, writing on “Curl” in potatoes, recommended that a sample of the seed-tubers intended for planting in the following season should be planted in a hot-bed before Christmas, and that if 2 per cent, or more of the plants exhibited Curl, the stock should be destroyed.