622 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



O. Appel^ (1903), and others as Schwarzbeiningkeit. The associa- 

 tion of *' Leaf curl " with a bacterial disease of the potato has been 

 recently investigated by Steglichf (1909). 



In Blackleg the haulm of the young plant becomes blackened just 

 above the level of the soil. The discoloration spreads, and ultimately 

 the lower portion of the stem rots and falls to the ground. During 

 the progress of this disease in the haulm the foliage goes through 

 a sequence of changes — first the foliage becomes yellowish and 

 the leaflets become more or less rolled or curled, then the leaves 

 droop and wither, and finally, sooner or later, depending on the 

 condition of the haulm, the foliage falls and rots. The black rot 

 extends in both directions from the haulm, by means of the vascular 

 bundles, upwards into the stem and downwards into the young tubers. 

 The disease appears in the tuber as a dark ring at first — observed by 

 Erwin Smith in 1896 — owing to its being confined to the vascular 

 bundles. This phase of Blackleg has been called ** Eing disease " 

 (Ringkrankheit). The affected tubers ultimately rot. In every case 

 the unhealthy plants produced very few tubers of small size. The 

 disease appeared to the greatest extent among plants grown from seed 

 raised on the farm in the previous year. 



The markings in the tuber due to Blackleg differ entirely from 

 those characteristic of Internal disease and Streak-disease. | In 

 * ' Eing disease ' ' the markings in the tuber follow the course of the 

 vascular bundles ; in the other forms of disease the markings do not, 

 as a rule, follow the course of the vascular bundles. Again, " Leaf 

 curl " is not a characteristic symptom of Internal disease and Streak- 

 disease, but there is no reason why plants thus affected should not 

 sometimes bear rolled or curled leaves. 



The symptoms of Blackleg in the Oleadon district may be sum- 

 marized as follows : — ■ 



^Symptoms not Leaf roll" or /'Leaves more or 

 confined to 



Blackleg 



= Schwarzbeinigkeit 

 = Black Stalk-rot 

 (G. H. Pethybridge§) 



Blackleg 



Symptoms 

 more or less 

 ^constant 



" Leaf curl 

 (Blattroll- 

 krankheit) 



/Blackleg 



less rolled or 

 curled — ulti- 

 mately droop 

 and wither. 



Local rot of 

 haulm, rot 

 spreads and 

 foliage col- 

 lapses. 



' Eing disease" jEing of blackish 



(Eingkrankheit) 

 and black rot 



spots in tuber. 

 Partial or com] 

 plete rot of 

 tuber. 



*Appel Bcr. d. Jhutsch. hot. Gcs., Bd. xx. p. 128 (1902). 

 t Steglich. L.c. ante. 



: A. S. Home. Jour. Agr. Sci., III. pt. 3 (1910), pp. 322-32. 

 § G. n. Pelhybridge. jour. Dep. Agr., Ireland, x. No. 2 (1910); G. H. 

 Pethybridge and P. A. Murphy. Proc. Roy. Irish Acad. xxix. B. No. 1 (1911). 



