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Summary

The interval which elapses between inoculation of tomato leaves with tomato aucuba mosaic virus and movement of virus into the stem varies considerably. Movement out of young apical leaves appears to be more rapid than that out of mature basal leaves, but the major source of variation is inherent in the individual plant and is not eliminated by standardizing the temperature and light of the environment. Since the time when virus enters the stem cannot be estimated accurately on any one plant, no precise estimate can be formed as to the rate of movement in the stem. Movement may be upwards or downwards. Discontinuity of virus distribution in the stem has been observed and this could be adduced as evidence against autocatalytic spread of virus; on the other hand, in other experiments virus appears to have been intercepted in its passage through the stem, which might make rapid transport through the phloem seem unlikely. This approach to the problem is insufficiently precise either for estimating the rate of movement of tomato aucuba mosaic virus through the plant or for determining its path.