DISEASES OF PLANTS. 249 



This disease, wliicli aiipears to he rather widely sjiread in the T'liited States, 

 has thus far not occasioned any great amount of loss. It resembles the disease 

 known as blackleg in Germany, which is attributal by ApiKjl to BaciUiii^ iilnj- 

 1(>l)hth(iruH (E. S. II., 15, p. 374), and the organism isolated resembles to a con- 

 siderable degree B. sohmisapnis, described by Harrison (E. S. 11., IS, p. 646). 

 The relationship between the different bacteria and the diseases they cause on 

 the potato is not considered in the bulletin. 



The disease, as the name indicates, is characterized by a pronounced black- 

 ening of the stem below ground, usually extending 1, 2, or even 3 in. above the 

 surface. Where conditions are very favorable, as during continued wet, cloudy 

 weather, the inky-black discoloration may be found on a portion of the stem 

 for several inches above the ground. 



Such losses as have been experienced in ]\Iaine are largely contined to the 

 killing of the affected plants before the tubers have reached merchantable size, 

 little or no decay of the mature tubers having been observed. 



The organism is distributed through the seed tubers, and it is recommended 

 that these be obtained from regions known to be noninfested. All cracked and 

 injured tubers should be rejected and tlie others treated with corrosive sub- 

 limate or formalin before cutting. 



The leaf roll disease and the bacterial ring- disease of the potato, W. von 

 Zkdtwitz (Wiener Laiidtr. Ztff.. '>'.> (1909), Xej. SS. pp. 87N, Sl9: <ihs. in Cnilhl. 

 Bakt. [etc], 2. AM., 26 (1910), 'No. J,-5, pp. Ill, iiS).— The author claims that 

 these two diseases are not identical, since their causes aiad symptoms are dif- 

 ferent and plants do not have both diseases at the same time. 



In the leaf roll disease the fungus is supposed to be a Fusarium, which 

 causes the leaves to roll and shrivel and reduces the yield materially, both in 

 quantity and size of tubers. The infected tubers are only about one-half their 

 normal size and are soft, while seed potatoes that are apparently healthy are 

 capable of infecting the crop grown from them. 



On the other hand, the bacterial ring disease does not seem to diminish the 

 yield or the size of the potatoes, nor to blight the tops of the plants, for tall 

 plants with large yields and potatoes which are rich in starch are the ones 

 usually diseased with the bacterial ring rot, as is shown by the brown areas 

 in the fibro-vascular bundles. This disease is apparently favored by loamy, 

 chalky soils, rich in humus. For its control the author recommends well 

 fertilized fields, fall plowing by means of steam engines to leave the surface 

 rough for the lietter aeration of the soil, careful selection of seed potatoes, 

 planting the seed whole, and thorough cultivation of the crop. 



The leaf roll disease of the potato, O. Reitmair (Ztschr. Laudiv. Tersuchsiv. 

 (Jsterr., 13 (1910), No. 1, pp. ^8-62). — From close observation in the field and 

 from the study of a large number of specimens of diseased plants collected in 

 diffei-ent localities, the author has reached the following conclusions : 



There is no specific death, shrivelling, or discoloration of any organ or 

 tissue of potato plants attacked by the I'eal leaf roll disease of Appel. When 

 such does appear, it is produced by other diseases which may be associated 

 with the leaf roll disease. If any biological changes occur in the conducting 

 tissues of the roots and stems, they are probably due to the rolling of the 

 leaves rather than to any real characteristic of the disease. 



In the genuine leaf roll disease, the primary root system has a stunted 

 growth. The laterals are brownish yellow and often crooked with few branches, 

 while the healthy plants produce juicy, thrifty, thick roots, with an abundance 

 of rootlets. This characteristic stunted appearance of the roots and stem 

 parts, the later rolling of the leaves, and the often observed coloring of the 



