Abstracts. 311 



The species treated were 



Aphis viburniphila n. sp. 

 Aphis rumexicolens n. sp. 

 Aphis saliceti Kaltenbach 

 Appiis davisi, new name 

 Prociphilus approximatus n. sp. 

 Prociphilus xylostei de Geer 

 Lachnus rosae Cholodkovsky 



STUDIES UPON THE BLACKLEG DISEASE OF THE 

 POTATO. WITH SPECIAL REFERENCE TO THE 

 RELATIONSHIP OF THE CAUSAL ORGANISMS.* 



This paper may be roughly divided into two parts. The 

 first part gives a brief historical review of the subject, describes 

 the character and appearance of the disease, its geographical 

 distribution and economic aspects, sources of infection, means 

 of distribution, and control measures. The second part, is 

 concerned with an investigation of the causal organisms, and 

 contains the results secured from a comparative study extend- 

 ing over a series of years. 



While the fact that the potato is subject to maladies like 

 that under consideration was noted at a comparatively early 

 date in the history of bacterial diseases of plants it was not 

 until about 1897 that blackleg was definitely connected with a 

 bacterial parasite. Since 1902 a number of dififerent investiga- 

 tors in Europe and one in America have isolated, described 

 and named as separate species, bacterial parasites associated 

 with and found capable of causing the type of potato disease 

 known as blackleg. 



Blackleg is a disease of both the stem and tuber. The 

 attacked stems are characterized by an inky-black discoloration 

 starting from the base, at the junction with the seed piece. 

 Usually the blackening extends only to the surface or at the 

 most only a few inches above the surface of the soil. Under 

 favorable weather conditions it may follow up the stem for 

 several inches, or even out on the larger branches destroying 



*This is an abstract of a paper by W. J. Morse, having the same 

 title and published in the Journal of Agricultural Research, V^ol. VIII, 

 No. 3, pp. 79-126. January 15, 1917. 



