SummaryThe contents of healthy cells and those infected with a number of different, plant viruses are described. Some of these viruses apparently do not cause the production of intracellular inclusions; others cause the production of amorphous bodies only, and the remainder produce both amorphous and crystalline inclusions. The properties of the inclusions are compared with those of purified preparations of the viruses. It is shown that insoluble complexes of the viruses with protamines, histones and proteins which in many ways resemble the intracellular inclusions can be producedin vitro.Possible explanations for the formation and disappearance of the inclusions in infected plants are suggested.