10 Proceedings of the Royal Irish Academy. 



in common use in this country for a disease prevalent among cattle, it seems 

 strongly advisable, in order to avoid confusion, not to use the term " black- 

 leg " for the present disease ; and we have, therefore, decided to distinguish it 

 by the name of " Black Stalk-rot." It may be stated that, amongst farmers in 

 general in this country, this disease has not hitherto been known by any 

 distinct name — probably because no particular attention has been paid to it. 

 In the west, however, plants sufifering from the disease are often said to be 

 " haughed " ; but the same term is perhaps more frequently applied to plants 

 which are .suffering fi'om the "Stalk Disease" caused by the fimgus 

 Sclerotinia sclerotioriim Massee. Formerly, before the disease was perhaps 

 fully recognized as being one sui generis, it lay hidden along with some 

 others under the somewhat indefinite description of " yellow blight." As 

 has, however, recently been poiuted out by one of us (23), the " yellow blight" 

 proper or the " yellowing " of the potato is a condition of the plant involving 

 a state of disharmony with its non-living environment, and is not a disease 

 due to bacterial or fungoid parasites. 



Black Stalk-rot makes its appearance early in the season — indeed it is, 

 perhaps, the earliest to appear of all the diseases to which the potato is subject 

 in this country, coming considerably before the bhght {PlnjtopKthora) arrives, 

 or has, at any rate, made any headway. It may be seen as early as the 

 second week in June ; but its appearance may be later than this. Affected 

 plants catch the eye as they stand distiibuted in a more or less scattered 

 and isolated fasliion through the drills or ridges. They stand out most often 

 perhaps owing to the lighter colour of theii- foliage as compared with that of 

 the neighboiu'ing healthy plants, and. as a rule, by their somewhat more stimted 

 growth. The foliage is very frequently yellow or, in the earlier stages, of a 

 lighter green than normal ; and it is sometimes more or less spotted. The 

 leaflets, particidarly of the yoimger leaves, are fi'equently folded along then- 

 michibs, and exhibit symptoms resembling " leaf-roll," although this is not 

 always the case. The uppermost intemodes of the stem frequently remain 

 short and imdeveloped ; while the leaves often assume a rather stiff, semi- 

 vertical position, instead of spreading out more or less horizontally. 



Frequently no signs of disease are to be seen on the portion of the stalk 

 itself above ground, although sometimes that part of it near the siu-face of the 

 soU is somewhat discolom-ed or blackened. If the stalk be pulled, it will be 

 found to come away easily, showing that the sti'ength of its anchorage in the 

 soil is but slight. The undergi-ound part of the stalk, or, at least, portion of 

 it, will be found to have decayed away, very often leaving strands at its 

 lower end, which consist of the more resistant vascular tissues of the stalk 

 lu some eases the entire cortical and other tissues of the stem outside the wood 



