PethybriDGE — The Verticillium Disease oj the Potato. 67 



(Krauselkrankheit). When the present investigation was started, the 

 account given by these authors was practically the only one dealing in detail 

 with the Verticillium disease ; and although during its progress some 

 additional information concerning it has been published, such as that by 

 Spieckermann and by Orton, which will be considered later on, yet Eeinke 

 and Berthold's work still remains the fundamental one on this disease. 

 Before proceeding further, therefore, it will be necessary to give a brief 

 resume of the account of the disease as given by these authors, laying stress 

 on those points which seemed to require further investigation before being 

 accepted as conclusively established. 



Beinke and Berthold describe the disease as making its appearance under 

 three distinct forms or types (A, B, and C). Type A is seen towards the 

 beginning of July, and is characterized by the wilting, drying up, and 

 yellowing of the lower leaves, not accompanied, at least to any extent, by 

 curling of the leaflets, or by brown spotting of the foliage. Fungus 

 mycelium is present in the wood vessels situated in all parts of the plant. It 

 is found in the new tubers, but is said never to proceed far into them, a 

 distance of fifteen millimetres from .the heel being the maximum observed. 

 It is stated to pass the winter at the point of detachment of the tuber from 

 its rhizome and partially within the tuber. 



Type B of the disease is seen at the same time as type A. Some time 

 after the middle of July, potato-stalks, which up to that time had appeared 

 perfectly healthy, begin to show a curling of the leaflets at their edges, and 

 brown spots begin to appear on the foliage. At length such spotted leaves 

 become completely dried up. The tissues of all the overground portions of 

 the affected stalks are completely free from fungus mycelium, but in the cortex 

 of those portions of them situated below ground and in that of the roots it is 

 stated that Verticillium albo-atrum is present. The fungus in this case also 

 reaches the new tubers, but by exactly what route is not clear from the 

 description. It is said to pass the winter as in the previous type at the very 

 heel-end of the tuber, and it could never be traced any distance into the 

 interior of the tuber. 



Although the two types mentioned are generally well marked and were 

 described separately, the authors admit that they occur not infrequently on 

 different stalks of one and the same plant, and even sometimes on one and the 

 same stalk. It is also admitted that in certain cases of type B of the disease, 

 mycelium was found after a time in the vessels of the stalks. It may be stated 

 at once that in the present author's opinion mycelium would probably always 

 have been found in the wood vessels of all parts of plants affected with type B 

 of the disease had the search for it not been made too early. Types A and B 



