70 Scientific Proceedings, Royal Dublin Society. 



This author, however, does not provide any experimental evidence in favour 

 of his contention ; and the observations and experiments now to be described 

 show that these views do not hold good. 



In 1909 a large tuber, nearly thirteen centimetres long, borne by an 

 affected plant, was subjected to microscopic examination by means of sections 

 of the vascular tissues removed from it, at intervals, in such a way that the 

 use of the tuber, or rather portions of it, as " seed " for the following season 

 would not be interfered with. By this means the mycelium was traced 

 definitely in the vessels of the tuber to a distance of 4 em. from its heel-end, 

 and the browning of the woody tissue was visible to the naked eye for 

 a distance of about 1.5 cm. beyond this point. Owing to the comparatively 

 small size of the vessels, and the difficulty of cutting hand-sections accurately 

 transverse to their long axis in the rose- end region, it was not possible to 

 demonstrate with certainty the presence of mycelium in them by this 

 method ; but it was noted that the walls of these vessels appeared, under the 

 microscope, distinctly browned, although this was not evident to the naked 

 eye. 



This tuber was, in the autumn, cut transversely into two portions, the cut 

 being made some distance nearer to the rose-end than the point to which the 

 mycelium had definitely been traced. The heel-end portion had two eyes on 

 it, while the rose had three. In the spring of 1910 the two halves were so 

 cut that five sets were available, each containing one eye. These sets were 

 planted in sterilised soil, each in a separate pot. Sets 1 and 2 were from the 

 heel-half of the tuber in which the mycelium was known to be present, while 

 Sets 3, 4, and 5 were from the rose-half in which the presence or absence of 

 mycelium was doubtful in the autumn. It could not, at any rate, have 

 reached them during the winter from the heel-portion of the tuber because 

 this had already been cut off in the autumn. 



The five sets were planted towards the end of April, and all of them 

 except No. 3 produced small plants which up to the middle of July showed 

 no symptoms of any disease. Set No. 3 was totally destroyed by a soft- 

 rot apparently of bacterial origin, while the plant derived from Set No. 4 

 was practically destroyed by an attack of caterpillars. As time progressed 

 little or no signs of rolling were observable in the leaflets of the plants ; but 

 the lower leaves began to wither and dry up ; and before the end of August 

 all three plants were practically dead, having succumbed to a progressive 

 desiccation proceeding from below upwards. Microscopical and cultural 

 examination showed that the vessels of these plants were completely choked 

 with the mycelium of Verticillium albo-atrum, which was also present in the 

 roots of the plant derived from set No. 4. In two cases (Nos. 1 and 5), in 



