Mode of Dissemination of Potato Virus X

VIRUS X is the commonest and most ubiquitous of all the potato viruses, but every attempt to discover an insect vector or other natural method of spread has failed. It has now been found, as a result of three experiments carried out in 1937, that it spreads freely from potato plant to potato plant under controlled experimental conditions by leaf contact, especially that brought about by air currents, without the intervention of instruments or human agency, and in circumstances excluding insect participation.