64 Scientific Proceedings, Royal Dublin Society. 



were being studied simultaneously, but more especially because it was found 

 that in order to obtain accurate information upon the extent and mode of 

 transmission of the disease by affected plants to their progeny it was necessary 

 to extend the observations over several successive seasons. Failure to do this 

 by earlier workers has resulted in somewhat incorrect notions regarding the 

 disease. 



II. Symptoms and Cause of the Disease. 



The case of the disease which formed the starting-point of the present 

 investigations was met with on a farm in Co. Dublin in the first week of 

 August, 1909. The plants were of the variety Duchess of Cornwall (a type 

 of Up to Date), and were being grown in a small plot. 



The affected plants, which were distributed promiscuously through the 

 plot, were of fair size, certainly not dwarfs, but not so large as their healthy 

 neighbours. They were clearly distinguished from the healthy plants by the 

 fact that their lower leaves were brown, shrivelled, and practically dead. The 

 upper, younger internodes of the stalks had failed to elongate normally, and 

 the leaves borne on them were more or less crowded together, forming a kind 

 of rosette. The individual leaflets of these upper leaves were folded upwards 

 and inwards on their midribs, consequently exposing their lighter-coloured 

 under-surfaces to view. 



On cutting the stalks transversely, the wood of three principal vascular 

 bundles was seen to be discoloured, being of a yellowish brown tint and not 

 so dark as is usually the case in attacks of Black Stalk Eot due to Bacillus 

 melanogenes. On pulling the stalks from the ground, it was at once clear that 

 the disease was not Black Stalk Eot, because the portions of them near the 

 surface of the ground and below it were not black and rotten, but, externally 

 at any rate, apparently quite healthy. 



The parent tubers from which the diseased plants had sprung were, in the 

 cases examined in detail, already rotten ; but it may be stated here that such 

 tubers do not always decay in this manner, for very often they may be found, 

 at the close of the season, hard and apparently sound. 



Amongst the newly formed tubers rather small-sized ones predominated, 

 although a few quite large ones were sometimes also present. The total 

 yield from the diseased plants was considerably less than that from the 

 neighbouring healthy ones. The tubers produced by the affected plants 

 showed no external signs of any disease. "When, however, these tubers were 

 cut across at their heel (proximal) ends, most of them showed a brown, dis- 

 coloured vascular ring, due, as subsequent microscopical examination showed, 

 to the browning of the walls of the elements of the wood, and, in the region 



