BLACK ROT OF THE POTATO: TYPE 257 



my top-inoculated plants have I seen any strong tendency of 

 the disease to extend into the tubers such as we see in case of 

 potato shoots inoculated with Bacterkmi solanacearum. The 

 disease occurs in its worst forna during warm moist summers and 

 autumns, but may continue on the tubers through the winter, if 

 the temperature in the store-houses or pits is sufficiently high. 

 In the tubers, the disease does not begin in the vascular ring 

 (contrast with No. IV). In the laboratory raw potato tubers 

 may be rotted very quickly (contrast again with No. IV) by 

 streaking the organism on their cut surface (Fig. 201). Lenticel 

 infections occur on the tubers (Fig. 202). Starch is not de- 

 stroyed and the infection is chiefly intercellular (Fig. 203). 



Dr. Appel's principal studies were made upon the potato 

 but he also isolated his organism from diseased comfrey {Sym- 

 phytum officinale). He successfully inoculated it into yellow 

 lupins, horse beans {Vicia faba), green tomato fruits, slices of 

 raw carrot, etc. 



This disease occurs all over Germany, in Ireland, and in 

 various parts of the United States (Maine, Virginia, South 

 Carolina, Wisconsin). Its distribution is probably co-extensive 

 with the culture of the potato, and I now regard it as one of the 

 most serious diseases of the potato. 



Cause. — The basal stem-rot is due to Bacillus phytophthorus 

 Appel (not sufficiently distinguished from Bacillus carotovorus 

 Jones, which name is earlier). This is a white, rapid-growing, 

 non-sporiferous. Gram negative, motile, peritrichiate-flagellate 

 (Fig. 204), promptly liquefying, nitrate-reducing, aerobic and 

 facultative anaerobic, acid-forming, gas-forming (but not in 

 the potato), milk-curdling (by formation of an acid), alkali- 

 tolerant, sodium chlorid-tolerant, chloroform-tolerant, dry- 

 air-sensitive, rod-shaped or filamentous schizomycete, forming 

 quickly on agar-poured plates circular, grayish white or, by 

 transmitted light, slightly bluish white, well-developed colonies; 

 and on very thin-sown gelatin plates characteristic, rapid-grow- 

 ing, big, circular (Figs. 205 and 206), opaque- white, fringed 

 (fimbriate-margined) colonies (Fig. 207), floating in a pit of 

 liquefaction (thick-sown plates liquefy too rapidly for these 

 examinations). The buried colonies in gelatin plates appear as 



