Pethybridge — The Verticillium Disease of the Potato. 73 



Verticillium emanating from the wood vessels and the coarse mycelium of 

 Hypochnus covering the cut surface. 



In the autumn of 1914 twenty -five tubers which were proved conclusively 

 to contain the fungus, by testing as above described, were selected. In the 

 third week of October, i.e. soon after they were dug, these tubers were each 

 cut into two portions, a heel portion and a rose portion, each possessing eyes, 

 the heel portions being as a rule larger than the corresponding rose portions. 

 The fifty sets thus obtained were then indelibly marked with Indian ink, so 

 that they could not possibly become mixed. They were placed in a sprouting 

 box and allowed to remain there over winter. In the spring all of them had 

 produced normal sprouts from the various eyes. 



In January, 1915, a further set of twenty- five tubers was selected which 

 were found on testing as before to contain the fungus. These were also 

 allowed to sprout in a box, which they did in normal fashion. In April, a 

 day or two before planting, these tubers were each cut into two portions, 

 roses and heels respectively. The tubers cut in the autumn and in the spring 

 were all selected from the same lot, and were the produce of affected plants 

 grown in 1914. 



At planting time in 1915, therefore, there were sets from twenty-five 

 autumn-cut tubers, and a similar number from spring-cut ones. Five pairs 

 of each were grown in pots in Dublin in a cool greenhouse, while the 

 remainder were planted at Clifden. No farmyard manure was used in either 

 ease. The resulting plants, some of which were diseased and some healthy, 

 were carefully examined for the presence or absence of mycelium in their 

 stalks. In the cases of the healthy plants, where no mycelium was found, 

 they were allowed to grow until the close of the season, when they were 

 dying naturally, so that the absence of mycelium was not due to the plants 

 having been examined too early. 



A summary of the results is given in the following table : — 



m2 



