90 Journal of Agricultural Research voi. xxn, ko. n 



illustration of any of a number of stem-end tuber-rots (PI. i6, A, B). 

 When a Netted Gem tuber of pointed shape affected with this type of 

 the disease is cut open longitudinally as soon as it is removed from the 

 ground, four distinct regions of decay may, as the rule, be seen: (a) 

 The extreme stem-end region is usually decayed throughout ; it is mushy 

 or slimy in consistency and dark brown to black in color ; in the field this 

 seldom extends deeper than the outer demarkation line of the decay, 

 but in storage under favorable conditions the disintegration advances 

 more rapidly in the inner tissues of the tuber, taking on a cup-like shape 

 and leading ultimately to the formation of a slimy cavity (PL A, 4; 14, B, 

 D; 16, B). (6) An area of fresh decay appears within the core just 

 beneath the first region; it is practically colorless, though it occasion- 

 ally contains dark or black streaks, and in the very early stages it has 

 the consistency of hardened butter (PI. A, 4). (c) The cambium layer 

 shows a brown discoloration extending sometimes close to the eye end; 

 in advanced stages a portion of this region nearest to the stem end is 

 more or less disintegrated and forms a channel attentuating toward the 

 eye end until it gradually transforms into a mere browning of the vas- 

 cular network which also gradually loses its intensity and finally disap- 

 pears altogether; this condition is very distinct with some freshly dug 

 tubers, but later on with the inward progress of the decay it becomes 

 less pronounced (PI. A, i, 4; 16, B), {d) The decay of the outer layer 

 develops in the bark region, is soft but not mushy in consistency and 

 more or less dark-brown in color; it frequently extends over the tuber 

 much farther than the pith decay, but not always as far as the cambium 

 discoloration; its progress is checked after tubers are dug and exposed 

 to drying (PI. A, i, 2; 16, B). 



2. The shallow stem-end rot of round-shaped tubers. This type was 

 observed mostly on the Idaho Rurals. Under conditions of abundant 

 moisture the bacterial infection spreads from the stem end over the 

 surface of the tuber and penetrates into the bark region, though not 

 very deeply. When such tubers are taken out of the ground and exposed 

 to the sun, as happens at digging, the infected areas dry up very promptly 

 and form hard, black, shallow patches (PI. 16, E). The condition may 

 easily be mistaken for the black fieldrot described by Pratt (6) and 

 attributed to Fusarium radicicola. If, however, the tubers are again 

 transferred to a moist place with a moderate temperature, a soft, mushy 

 bacterial decay is likely to develop beneath these dry areas. On the 

 contrary, under conditions unfavorable to the blackleg decay the status 

 may either remain unchanged or become complicated by the entrance 

 of various Fusaria and other rot-producing fungi. In the latter case it 

 is impossible to determine the original cause of the disease. 



3. Siderot of either round or long potatoes. It may penetrate inside 

 of the tuber to a considerable depth, and when a freshly dug diseased 



