18 BULLETIN 6i, U, S. DEPARTMENT OF AGEICULTUEE. 



trouble here described as "curly-dwarf" (Ki'auselkrauklieit) . He 

 emphasizes the rolling of the leaves, but does not mention that they 

 wilt. The discoloration of the vascular bundles of stem and tuber 

 is remarked, and experunents are cited which show that the disease is 

 transmitted through affected seed tubers. 



The same author (1912) further illustrates the distmction between 

 curly-dwarf (''curl") and leaf-roll, and reports havmg found cases 

 of leaf-roll m which no VerticiUium or other fungus was present. 

 Tubers from such plants gave rise to healthy plants, whence it is 

 concluded that the occurrence of the true leaf-roll m Ireland is not yet 

 established. 



These facts, together wdth his personal observation in Great 

 Britam in 1911, led the writer to beheve that no cases of true leaf-roU 

 or of Fusarium wilt have yet been proved to occur in Great Britian, 

 but that VerticiUium wilt is not uncommon there. 



Some confusion stdl remams concernmg the parasitism of Verticil- 

 Hum alho-atrum, inasmuch as there are many reports of its occurrence 

 where the marked pathological effects here described were not present. 

 Reinke and Berthold report successful inoculations, and WoUenweber 

 obtained infections in Friedenau, Berlin, which, m the light of his 

 later work, are to be considered as added evidence of the parasitism 

 of this species. The result of 'a later successftd infection experiment 

 performed by WoUenweber with pure cultures in the Washington 

 greenhouse is shown in Plate III. The parasitism of VerticiUium on 

 other plants has also been demonstrated by hun and will soon be 

 pubhshed m fuU. It is not to be understood that the relatively minor 

 role now played by VerticiUium as a potato parasite in the United 

 States indicates that it is a disease that should not be feared, for, if 

 control measures are neglected, it might easily become epidemic and 

 as destructive as the Fusarium wilt. 



The disease should be easUy brought under control, however, by 

 seed selection and rotation of crops. Whenever a wUted hill is 

 observed in a field it should be taken up and both vmes and tubers 

 carried out and destroyed. When cuttii;ig seed, any with a brown 

 stain at the stem end should be rejected. When a field is much 

 affected by this trouble, none of the crop should be used for planting, 

 and the ground should be given a longer rotation than usual. 



LEAF-ROLL. 



LITERATURE OF THE DISEASE. 



No plant disease in this generation has been the subject of such 

 general discussion as that known m Germany as the "BlattroU- 

 krankheit," herein named "leaf-roU. " None has aroused greater 

 difference of opinion as to its nature and cause, and no other single 

 malady of plants is to-day receiving so much investigation by skilled 



