Family Solanaceae 309 



shovild not be mistaken for a temporary rolling of the 

 leaves that may be brought about by excessive 

 humidity in poorly drained lands. Heat, drought, 

 and excessive use of fertilizers, especially potash, may 

 bring about a temporary leaf rolling. Leaf roll is 

 prevalent in Germany, Austria-Htmgary, Switzer- 

 land, the Netherlands, Denmark, and Sweden. In 

 the United States it is found in Eastern Colorado, 

 Western Nebraska, Virginia, and Maine. Since the 

 trouble is carried with the seed, this should be 

 secured from localities known to be free from the 

 disease. 



Curly-Dwarf 



Cause Unknown. 



This disease differs from leaf roll by a dwarfed 

 development of the plant, and a wrinkled and down- 

 ward curling of the leaves (fig. 58 b), resembling the 

 natural curling of the foliage of kale or Savoy cab- 

 bage. A peculiarity of this disease is that the mid- 

 ribs, veins, and leaf petioles together with stems and 

 branches are all dwarfed, giving the foliage a thickly 

 clustered appearance. The foliage keeps its normal 

 color and turgidity. There is also a tendency for the 

 plant to send out numerous branches with brittle 

 stems. The effect of the disease is to reduce the 

 yield, and in severe cases there is an absence of tuber 

 production altogether. Like leaf roll the disease 

 is transmitted with the seed tubers, but it does not 

 spread from plant to plant. The trouble is prevalent 



