204 Scientific Proceedings, Royal Dublin Society. 



no special association with the " vascular ring." Affected tubers often show 

 a few cavities more or less completely filled with mycelium, which, however, 

 as a rule, does not in these circumstances bear many conidia or chlamydo- 

 spores. The newly killed tissues are still moist, more or less yellowish in 

 colour, and of a granular consistency. The line of demarcation between the 

 diseased and healthy tissues is not always strongly marked when an affected 

 tuber is first cut open, but on standing exposed to the air the diseased portion 

 gradually becomes distinctly browned. 



In the interior of a completely rotted tuber, cavities containing a luxuriant 

 growth of mycelium are also present. The mycelium lining the walls of these 

 cavities is frequently distinctly blue ; and very often this colour also pervades 

 the dead tissues for some little depth around the cavities. The intervening 

 portions of the dead tissues are, at this stage, of a dirty white colour, and 

 are more or less easily reduced to powder on being rubbed between the 

 fingers. 



Microscopical examination of sections made at the junction of the diseased 

 and healthy tissues reveals the presence of branched, septate mycelium 

 between the cells of the diseased tissues. In the completely browned and 

 nearly dry, dead tissues, however, the mycelium is found to be both intra- 

 as well as intercellular. The starch grains remain unattacked. 



The fungus pustules present on the wrinkled skin are not arranged in 

 any definite order or system, nor are they all absolutely alike, either 

 as regards shape and size or colour. They are, as a rule, white on their 

 surfaces ; but if the outer layers be rubbed or scraped away, or if the 

 pustules be sectioned, their bases are seen to be deep blue in colour. 

 Occasionally the pustules are superficially blue, while they may also be 

 distinctly pink, especially if the rotting tubers have been exposed to a good 

 light. 



The base of each pustule is made up of a compacted mass of hyphae 

 running more or less at right angles to the surface of the tuber, and blue in 

 colour. From this base a very large number of blanched conidiophores 

 bearing septate, fusiform conidia arise. The conidiophores are illustrated in 

 fig. 1, Plate VII. The ultimate branches of the conidiophores (sterigmata) 

 are somewhat swollen, more or less fusiform cells. At the apex of each 

 sterigma, after the first and each subsequent conidium has been formed, 

 there remains a not-easily-discerned, slightly funnel-shaped, projecting, 

 empty sheath or collar, formed from the cell-wall at the point where the first 

 conidium and the sterigma part company. 



The base of each succeeding conidium remains for a longer or shorter 

 period within this sheath, and, doubtless, it is this fact (as we found Appel 



