180 



Scientific Proceedings, Royal Dublin Society. 



fumigator, the chimneys being removed. The pots were then filled up with 

 sterilized soil, so that the sprouts were covered, and the plants were allowed to 

 develop. They were divided into four lots, depending on the probability of 

 successful infection, which were separated a considerable distance from each 

 other out of doors on the flat roof of the College of Science building in the centre 

 of Dublin. The plants were kept under close observation, and whenever, as 

 happened, a few aphides appeared on the foliage of any of them, they were all 

 fumigated again, still in separate lots. That these aphides can have had no part 

 in the successful infections which followed is clear J'rom their insignifieant 

 numbers and immediate suppression; from the early development o£ ]eaf-roIl; 

 from the fact that the disease appeared at once in the secondary form; and 

 from the unexceptional behaviour of the control plants. 



MOSAIC 



The results of the experiment are diagrammatically represented in the right- 

 hand iDortion of the figure already alluded to. The original tuber was evidently 

 affected with leaf-roll from the beginning, the resulting plant being badly 

 diseased. The leaf-roll disease was transferred from this to both the mosaic 

 half tuber and the healthy half tuber first infested, for the resulting plants 

 showed leaf-roll (secondary) combined with mosaic in the one case and leaf-roll 

 (secondary) alone in the other. The aphides taken from the former infected with 

 leaf-roll (secondary), two out of the three plants arising from healthy half tubers 

 on the sprouts of which they were placed. The third plant remained apparently 

 healthy; but it should be stated that observations ceased abruptly on June 26, 

 when the experiment had to be abandoned. Up to that date also leaf-roll had 

 not appeared in either of the two plants derived from healthy half tubers 

 on the sprouts of which aphides from the originally infested healthy half 

 tuber had been placed (second horizontal row from the top on right of 

 diagram). The third tuber in this row failed to produce a plant. In spite of 



