332 Ptianzenkrankheiten. 



influence of climate is demonstrated by the following facts: No 

 infections resulted on the progeny of powderry-scab-infected seed 

 potatoes planted in 15 different localities along the Atlantic sea- 

 board. However, 8 lots of soil out of, 12, shipped from as many of 

 these localities to northern Maine and planted with infected seed 

 produced a crop showing powdery-scub. The disease is always 

 most prevalent on wet, poorty drained land. Periods of damp, 

 rainy, and cloudy weather favor the development of 5. subterranea. 

 Numerous cases indicate that the disease can live in the soil for 

 more than three years, and from facts and hand the writers believe 

 that it can live for at least five years and probably much longer. 

 All Underground portions of the potato plant may become infected 

 with S. subterranea. Infection develops earlier on the roots than on 

 the tubers; on the tubers it appears about the stem end first. Galls 

 are often very numerous on the root System of potato plants grow- 

 ing in infected soil, while the tubers are absolutely free from infec- 

 tion. This leads to the conclusion that the critical test for the pre- 

 sence of the disease in a field is the freedom of the root System, 

 and that the roots and not the tubers are the organs of the plant 

 which determine the resistance of potato plants to the disease. 

 Besides the potato, there are seven other solanaceous hosts of 5. 

 subterranea , including the tomato. The disease manifests itself on 

 these hosts in the form of large destructive galls on the roots, 

 these being fully as injurious as those on the potato plant. The 

 histology of the galls on all the hosts is very similar and has many 

 points in common with Plasmodiophora brassicae on cabbage. The 

 absence of the canker stage of 5. subterranea in the United States 

 may be due to the short growing period afforded the potato crops 

 in infected districts. Among the saprophytic fungi found associated 

 with the sori of S. subterranea is a species of Papulospora, which 

 caused much confusion in earlier writings. Practical suggestions for 

 combating the disease are given, viz: early harvesting and seed 

 treatment; the possibility of finding a resistant variety has not yet 

 been exhausted No soil treatment will eradicate the disease, but 

 sulphur at the rate of 900 pounds per acre applied broadcast redu- 

 ces the amount of infection by S. subterranea. Several types of 

 dryrot follow S. subterranea. The percentage of these secondary 

 rots as found in nature in infected tubers varied from 30 to 70. 

 The most serious of these rots is a dryrot due to a species of 

 Phoma, designated by the writers as: „Phoma tuberosa, n. sp." 



Van der Lek (Wageningen). 



Pratt, O. A., A western fi eidrot of the Irish potato tuber 

 caused bv Fusarium radicicola. (Journ. Agric. Research. VI. p. 

 297—309. PI. 34-37. 1916 ) 



This paper is concerned with certain rots attacking the potato 

 tuber while growing in the field. Under the head of fieldrot are 

 considered several types of decay occurring in potato tubers while 

 yet in the field — a stem-end rot, a lenticel rot, and a rot pro- 

 ceeding from eye infections. The name „blackrot" best describes 

 them: a comparatively dry rot, dark to nearly black in color, pro- 

 ceeding from the stem end, lenticels, and occasionally from the 

 eyes of the tuber. It is confined principally to potatoes of the 

 round type. The jelty-end rot of the Burbank group is a soft, wet 

 rot of the tubers, light to dark brown in color, commonly a stem- 



