The results of the attempts here described to cultivate the incitant of mosaic disease of tobacco and tomato plants give good reason to suppose that this has been accomplished. The agent in the tissues of affected plants induces the disease not infrequently in a dilution of 1:10,000 but only very rarely at a higher dilution. During its transference from tube to tube of the special medium used in the present study it underwent a dilution far beyond these effective limits—in one experiment to 4 x 10–16. Nevertheless, the material of the remote subplants proved effective in inducing the disease, which appeared as rapidly and in as active a form as if the undiluted inoculum had been employed. Material derived from plants in which mosaic developed as result of inoculation with the culture fluid induced the disease in yet other plants, and from these again the agent could be propagated in vitro, or transfers to other plants could be made.

In the course of the experiments a significant fact was noted; namely, that the agent present in remote subplants which can induce the disease was not readily filterable. The nature of the change thus indicated remains to be determined. No formed elements could at any time be distinguished in the medium.

The conclusion seems justified that the incitant of mosaic disease of tobacco and tomatoes is a living microbic body which can be cultivated in an artificial medium.

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