80 Scientific Proceedings, Royal Dublin Society. 



In spite of prolonged culture on varied media, Verticillium albo-atrum has 

 not been found to produce any other reproductive bodies such as peritheeia, 

 nor has it ever produced chlamydospores of any kind. 



VII. Infection Experiments. 



The first attempt at producing the disease by suitable inoculation of a 

 healthy plant was made at Clifden in the summer of 1909. The inoculation 

 was made by inserting a portion of the woody tissue containing the fungus, 

 obtained from a diseased plant, into a freshly prepared wound made to the 

 depth of the wood just above ground-level in the stalk of a healthy plant, 

 taking precautions to avoid, as far as possible, contamination with other 

 micro-organisms. After nineteen days there were no distinct outward signs 

 that infection had occurred ; but as the foliage of the plant was beginning to 

 be destroyed with the ordinary blight, it was decided to break off the experi- 

 ment at this point. Sections of the inoculated stem showed the presence of 

 fungus mycelium in the wood vessels to a distance up the stem of twenty 

 centimetres from the wound ; and on suitable incubation it proved to be that 

 of Verticillium. Hence it appeared probable that there would be no difficulty 

 in transferring the disease by inoculation. 



In the foregoing case of course a pure culture was not employed, but in 

 1914 several series of infection experiments were made with pure cultures. 

 Those of the first series were carried out on plants in pots in the greenhouse 

 of the Seeds and Plant Disease Division of the Department of Agriculture in 

 Dublin, and were as follows : — 



The plants for the experiments were grown from previously sprouted 

 healthy tubers from which all the eyes except the strong terminal one were 

 excised. This was done in order that each plant might have but one sub- 

 stantial sprout or stalk suitable for inoculation. Inoculation was made in all 

 cases by introducing portion of a pure culture into wounds carefully made in 

 the sprouts or stems at a node, precautions being taken to prevent contamina- 

 tion by other micro-organisms. After inoculation the wounds were carefully 

 covered with tinfoil, and were thus not allowed to come into direct contact 

 with the soil. In every case where an inoculation was made a similar sprouted 

 tuber or plant was treated in the same way, except that no portion of a culture 

 was introduced into the wound ; and this served as a control. In this 

 particular series there were eight plants inoculated at four different periods, 

 together with their eight controls. Some of them were inoculated in the 

 sprouts before planting, others when the shoots were only about two inches 

 above the soil, and the remainder at correspondingly later dates. Symptoms 



