558 Scientific Proceedings, Royal Dublin Society. 



(P. infestans) was also small, beiug only about 0-7 per cent, of the total 



crop. 



Pink Eot was more prevalent on land which had borne two potato crops in 

 succession, being in weighable quantity, and present to the extent of about 

 0-6 per cent, of the total crop, while the blight on this land was responsible 

 for a loss of nearly 3| per cent, of the crop. 



On one piece of land which had carried a potato crop for four years in 

 succession the loss in twenty-four plots of one square perch each averaged 

 over 10 per cent., while the loss due to blight in the same plots was practically 

 negligible. The percentages by weight of tubers attacked with Pink Rot 

 in these plots varied very greatly, the lowest being 2-8 per cent., and the 

 highest 33'3 per cent. 



On another piece of land also cropped with potatoes for four years in 

 succession the losses due to Pink Eot were somewhat less, averaging just over 

 4 per cent., while those due to blight in the tubers was extremely slight. 



Hence it will be seen that the loss in tubers caused by the attacks of 

 P. erythroseptica may in certain cases be considerably greater than that due 

 to the attacks of P. infesfcms. 



The presence of the disease to a slight extent even in a crop grown on 

 freshly broken-up land is probably to be accounted for by the fact that some 

 of the resting spores of the fungus, doubtless adhering to the external surfaces 

 of the " seed " tubers which were obtained from crops on old, infected land, 

 were thus conveyed to the new land. The amount of infection, however, in 

 the first year is so small that treatment of the seed tubers with a disinfectant 

 before planting would probably not repay the necessary trouble and cost. 



It seems fairly certain that the disease cannot well be transmitted by the 

 presence of the fungus iciihin the seed tubers. The rot caused by P. erythroseptica 

 is such a rapid one that the tubers become entirely destroyed in a few days, 

 and therefore such affected tubers could not possibly remain alive over the 

 winter and be used for seed during the following year. 



Whether the disease can be communicated from affected tubers to healthy 

 ones by contact during storage is a point on which an experiment was started 

 last autumn, but the result cannot be stated, as the pit has not yet been 

 opened. 1 



It would appear to be quite easy to avoid the disease by planting only 

 tubers derived from clean land, and especially by following a proper rotation 

 of crops, and not growing Potatoes on the same land in successive years. 



' Since this was written the pit iias been carefully examined, and it was found that the disease 

 was not communicated from the diseased to the healthy tubers. 



