1923] 



JENNISON — POTATO BLACKLEG 



23 



vigorated culture in a depression, usually near an eye, and stab- 

 bing through the inoculum 3 or 4 times with a sterile needle. 

 The control tubers were pricked in similar places with a sterile 

 needle. Inoculation courts were marked with an indelible pen- 

 cil by tracing a good-sized circle around the spot where the tuber 

 was pricked. Check courts were marked by a square. 



i 



Observations and conclusions. — The inoculation sets thus pre- 



pared were closely observed 

 frequency for over a month 



day for 10 days, then with less 



The number of days elapsing before signs of infection were 

 visible varied, in the several experiments performed, from 2 to 



6 days. Infection 



general more prompt where tubers 



having a high sugar content were inoculated, where the 



cubated 



C, and where the moisture content of 



the atmosphere surrounding the tubers was kept high. Observa- 

 tions made by the writer on the pathogenicity of several strains 

 of the potato blackleg parasite suggest the conclusion that the 

 "incubation period" in plants is markedly influenced by environ- 



mental conditions 



incubation period" did 



be marked by a definite "turning point," as is the case in many 

 animal diseases. 



The writer concluded that all the strains being tested were 

 pathogenic (cf. tables i and n). The nature and development 



Cult. 

 No. 



200. 



201 



202 



TABLE I 



TABULAR SUMMARY 

 SOURCE AND HISTORY OF CULTURES USED 



160.1 



170.3 



180.2 



183.2 



187B . 1 



193 



194. 



195. 



196. 



197. 



198. 



Isolated 



Tuber 8-14-'15 

 Tuber 8-2 2-' 1 5 

 Stem 7-24-'16.. 

 Stem 8-27-'16.. 

 Tuber 9-2-' 16.. 



Source 



a 



it 



Plant" Aug. ,'08 

 Stem" Aug., '08 

 Plant" Aug., '08 



Before Mar., '09.. 



Before 1910 



By P. & M. 1911 



"Blackleg" 1915 



Before 1906 



About 1907 



Montana 



Montana 



Montana 



Montana 



Montana 



Maine, Morse's IIIA 

 Maine, Morse's SE... 

 Maine, Morse's IIP .. 

 B. sol. Ontario, Can... 



B. atro. Krai's lab. 



B. mel. fr. Pethy. Ire- 

 land 



Minnesota 



B. phyto. fr. Germany 

 B. sol. Am. Museum 



Marked 



Marked 



Strong 



Marked 



Strong 



Strong 



Yes 



Strong 



Marked 



Marked 



Yes 



No data 

 Marked 

 No data 



Strong 



Strong 



Marked 



Marked 



Strong 



Strong 



Yes 



Yes 



Marked 



Yes 



Yes 

 Yes 



Marked 

 Strong 



Comparative 

 virulence 



Average 

 Average 

 Average 



Average 

 Strong 



Average 

 Average 

 Average 

 Average 

 Average 



Low 

 Low 

 Strong 

 Average 



