114 MASS. EXPERIMENT STATION BULLETIN 175. 



bed, and as a rule those beds which have long been used or carelessly- 

 handled are found to be producers of mosaicked seedlings in far larger 

 numbers than are found on new beds or on beds which have been carefully 

 sterihzed either by steam or formalin. 



It has been found that the soils of old beds do tend to produce more 

 mosaicked plants than do those of new beds, although it may be possible 

 that under field conditions the differences in amount during different 

 seasons may vary. Soils brought into the greenhouse gave the following 

 results: — 



Table XIV. — Experiments with Soils from Old and New Beds. 



[Seedlings transplanted in sterilized soil.] 



The soil from the old beds was in very bad condition and had been 

 very carelessly handled, apparently. 



A count of mosaicked seedUngs left in these old-bed soils six weeks after 

 the transplants was taken, showing, respectively, an infection of A, 43 

 per cent.; 21, 32 per cent.; la, 17 per cent.; B, 6 per cent.; and C, 7+ 

 per cent. 



It is evident that some of the seedlings were infected during trans- 

 planting, probably by handling diseased seedUngs and then healthy ones, 

 thus transmitting the disease. This method of transmission at the time 

 of transplanting is very common, as has been pointed out repeatedly. 



It has been shown that much of our infection may originally come from 

 the seed bed as a result of the soil becoming infected for any reason. The 

 use of tobacco stems and tobacco water has also been found by many 

 investigators to cause infection. The amount of infection resulting from 

 watering beds with water extract of diseased stems is, however, prob- 

 lematical, and it is not believed by the writer that this is an important 

 factor in mosaic transmission, especially if the stems are steeped in hot 

 water. The broken, decaying roots of diseased plants left in the beds also 

 carry the causal agent of the disease as do the stems of diseased plants, 

 and freezing has apparently little or no effect on it, so the use of stems on 

 the seed bed should be carefully attended to in order not to apply any 

 from diseased plants. Where stems and tobacco water are applied year 



