90 Scientific Proceedings, Royal Dublin Society. 



not necessarily infected, although the great majority of them certainly are. 

 It has also been found that a small percentage of affected tubers may 

 produce healthy plants with sound progeny, so that with proper care it would 

 be possible in the course of a couple of seasons or so to raise a fresh stock of 

 healthy seed-tubers from a previously diseased one. 



It might be possible also to heat affected seed-tubers to a temperature 

 high enough to kill the fungus in the wood vessels without injuring the 

 vitality of the tubers themselves, as can be done with tubers attacked with 

 Phytophthora infestans ; experiments on this point are now being carried out, 

 but the results will not be known for some time. 



X. Summary. 



The Verticillium disease of the potato is one which results in the more or 

 less premature death of the plant, the general symptoms exhibited being 

 those of a process of gradual desiccation. 



The mycelium of the fungus Verticillium albo-atrum R. and B. is found in 

 the wood vessels of all parts of affected plants. It passes into the wood 

 vessels of the new tubers, and from these again, in the great majority of cases, 

 into the plants which develop from them. Hence the disease is transmitted 

 by means of infected tubers. The fungus in the tuber is not necessarily 

 strictly localized at or near the heel-end, as previous authors have supposed. 



The fungus grows well in pure culture as a saprophyte, and infection 

 experiments on healthy plants carried out with pure cultures were successful 

 in reproducing the disease. 



The disease was, to some extent at least, formerly covered by the 

 terms " Curl " and " Leaf-Roll," but it is now to be removed from this category, 

 and to be regarded as a specific type of those diseases in which the wood 

 vessels become infested with fungus mycelium and for which the general term 

 hadromycosis is suggested. 



The disease does not appear to be very common in the British Isles, and 

 the losses due to it are at present probably not large ; but should it become 

 prevalent, the losses might be severe. The most satisfactory preventive 

 measures are to maintain a proper rotation of crops, and to take steps to 

 ensure that the potatoes used for seed purposes are healthy. 



