86 Journal of Agricultural Research voi. xxh. No. » 



were identical for all strains. The writers regard their western strains 

 as nonchromogenic, although a certain yellow discoloration in cooked 

 potato cultures might be taken as a suggestion of yellow pigment. They 

 obtained no evidence of diastatic action on potato starch, nor of acid 

 production with glycerin. 



It may, therefore, be concluded on the basis of the characters described 

 that the pathogenic bacillus isolated by the writers from a peculiar soft 

 decay of western potato tubers is essentially identical with the organism 

 causing the blackleg disease of potatoes for which Appel's binomial 

 Bacillus phytophthorus is regarded to be correct by Smith (7) . Morse (5) , 

 who was unable to obtain an authentic culture of Appel's strain for his 

 comparative studies of various blackleg organisms, believed that 

 B. atrosepticus should be chosen in preference to other names he had 

 under consideration, but stated that — 



There is nothing in the data here presented which bears on the relation between 

 the organism originally described by Dr. Appel (/) as B. phytophthorits and the other 

 strains of blackleg bacteria. 



EXPERIMENTAL WORK 



The pathogenicity of the bacterial organism described above was 

 established by means of the following laboratory, greenhouse, and field 

 experiments. 



PLANTING OF THE ORIGINAL MATERIAL 



Preliminary to the inoculation work some of the diseased western 

 material was planted in the greenhouse as soon as the isolations were 

 completed. Four tubers were selected and cut in halves so as to make 

 eight seed pieces. Each piece was planted in a separate large pot filled 

 with sterilized soil. Of these seed pieces one decayed completely in the 

 soil before germination, six produced diseased plants, and one produced 

 a plant considerably weakened though not clearly diseased. Some of 

 the affected plants decayed while very young, others grew up to practi- 

 cally normal size, developing blackening of the stem above ground and 

 brown to black lesions on the underground portions. The lower leaves 

 turned yellow, but the upper leaves wilted while green. In two cases 

 the blackening of the stems was very intense (PI. 13, A) while in the 

 remainder the appearance was less typical of the familiar field symptoms 

 of the disease as it occurs in the eastern sections of the country. Black- 

 ening of the pith of the stem developed to the very top in one case. 

 When an affected plant was removed from the pot and the soil was care- 

 fully washed off, it could be seen that the infection had spread from the 

 seed piece to the stem (PI. 13, B). No tubers were produced in this 

 experiment. Healthy sprouting Irish Cobbler tubers were replanted in 

 these pots, but no infection was contracted by this new set of plants. 



