82 Scientific Proceedings, Royal Dublin Society. 



the characteristic symptoms of the disease, and they died off prematurely, 

 whereas the controls behaved normally. Microscopic examination of the 

 inoculated plants showed the fungus present in all their 'organs, including 

 some of the new tubers. Similar examination of the controls showed that ten 

 of them were quite free from the fungus. In the case of one of the remaining 

 two, it was found in the vessels of a single rhizome, but in no other portion of 

 the plant, and in the case of the other it was present in the vessels of some of 

 the roots. These two plants were growing in close proximity to two of the 

 inoculated plants, and it is quite possible that the rhizome and the roots may 

 have become infected by coming into contact with the diseased roots or 

 rhizomes of these neighbouring plants ; it would have been better if 

 the controls had been planted at a greater distance from the inoculated 

 plants. 



A further series of inoculation experiments was carried out in the field at 

 Clifden, there being four inoculated plants and four controls. Two of these 

 and the corresponding controls were on plants of the variety Up-to-Date, 

 which was the one used in the previously described series. The controls 

 remained perfectly sound, while the inoculated plants became diseased, and 

 were found to contain the fungus in all their parts, as in the cases already 

 described. 



The other two inoculated plants and the corresponding controls at Clifden 

 were, however, of the varieties Shamrock and Northern Invincible respectively. 

 Both of these varieties have proved themselves to be resistant to the attacks 

 of blight (Phytophthora infestans), the former very highly so and the latter 

 slightly less highly. The method of inoculation was the same as that 

 employed in the previous experiments. The plant of Northern Invincible 

 became diseased, and invaded in all its parts by the fungus, just as had been the 

 case with the Up-to-Dates, while some of the tubers also contained it. On the 

 other hand, the symptoms of disease in the inoculated plant of Shamrock 

 were less pronounced, and the invasion by mycelium was much less extensive. 

 The fungus was found in the vessels of the upper portions of the inoculated 

 stem; but just below the inoculating wound it stopped, and it did not proceed 

 further downwards. The roots, rhizomes, and tubers were found to be free 

 from it. Hence it would appear probable that this variety is somewhat 

 resistant to this disease, as well as to the blight. The controls in this case also 

 remained sound, and were found to be free from mycelium. 



Still further inoculation experiments were carried out on cut stalks 

 placed in Tollens' nutrient solution, and kept under observation in the labora- 

 tory. It is not necessary to deal with these in detail ; suffice it to say that 

 the fungus spread from the inoculating wound in the vessels, both up and 





