SUMMARYOnly a small percentage of tomato plants became infected when grown in soil that contained TMV‐infected debris from a previous crop, whether they were set out into this soil or into a layer of partially sterilized soil overlying it. In one experiment, half the plants were infected when grown in sand containing infected tomato debris, and treating the sand–debris mixture with metham‐sodium greatly increased the proportion of plants infected. When shoots were separated from each other virus was not transmitted from adjacent infectors through roots of plants growing in uninfested soil.When roots were inoculated with TMV, virus was detected in young shoots after periods varying from 3 weeks in seedlings to 6 months in older plants, the average periods being between 10 and 16 weeks. Virus was detected in the roots of many plants, but not in their shoots, when experiments ceased 4–6 months after root inoculation. Plants infected in their roots often showed severe fruit defects in the lower trusses several weeks before mosaic showed in the