366 Scientific Proceedings, Royal Dublin Society. 



storage I'ot. This is seen especially by comparing pits 3 and 6 and pits 4 

 and 7. The corresponding pairs of plots had been dug on the same dates, 

 respectively. The difference consisted in that the foliage had been removed 

 from one each of the two pairs twenty-five days and thirty-three days before 

 digging, while it had not been removed from the other two. This operation 

 brought about two changes in the conditions, either of which might, 

 theoretically, be held accountable for the reduction in the disease. The 

 duration of the blight attack on the foliage was reduced, on the one hand, 

 and with it the supply of spores capable of being washed down to the tubers. 

 On the other hand, the contamination of the soil ceased, and a period elapsed 

 presumably sufficient for the spores present at or near the surface to lose 

 their vitality. 



It is not possible to apportion with certainty the exact influence of each 

 of these two factors. This is because the blight, instead of diminishing 

 gradually with the progressive death of the foliage, rallied from the low ebb 

 it had reached about the middle of September (when the first and second 

 diggings were done), and was more severe at the time of the third and fourth 

 diggings. Had it not been so, it was anticipated that there would have been a 

 gradual diminution in the amount of tnber disease found in storage in the 

 series of plots from 1 to 4, and a still more marked diminution in the series 

 5 to 7. Furthermore, the lifting of plots 4 and 7 liad to be hastened 

 owing to the exigencies of farm operations, although it was intended that 

 they should be left until well after the death of the foliage was complete. 

 A reduced amount of tuber disease was again anticipated from this 

 course. 



AVhile certainty was not attained, an examination of the evidence shows 

 that the probabilities are in favour of the theory of infection at digging time. 

 In support of this are the following points : — 



(1) All the plots went through a very severe blight attack, lasting from 

 the latter part of July until the end of August, with but slight injury to the 

 tubers (as measured by the amount of disease found in them when dug), at a 

 time when they were immature, and theoretically more susceptible to 

 infection. 



(2). The amount of blight found in the tubers in the field was slight and, 

 comparatively speaking, uniform ; and it did not vary directly with the date 

 of digging or with the length of the period during which the foliage was 

 allowed to stand. The variations were irregular, though not of great magni- 

 tude. The highest total of disease in the field was found in one of the plots 

 dug first, and the next highest in one dug nearly last, 



