SYMPTOMS OF CURLY-TOP. 



11 



INTERNAL SYMPTOMS. 



Certain distortions of the cells of the tissues of leaf and stem have 

 been observed in beets affected with curly-top; the fibro-vascular 

 bundles may become darkened throughout the entire length of the 

 root (PI. Ill, fig. 2). No decay or softening of the tissues has been 

 noted as a direct consequence of the disease ; on the contrary, the root 

 becomes tougher and more fibrous, thus rendering the slicing of the 

 beets more difficult, with frequent clogging of the cutters. In many 



Pig. '2. — Curly-top sugar beet, face of leaves, showing retracted type of curl. Disease 

 produced under test conditions by gradually increasing number of beet leafhoppers until 

 curl developed. Plant at start three and a half months old. 



roots a blackened area, or even a cavity with black walls, may be 

 found in the interior of the crown (27") (PI. Ill, fig. 2) ; this latter 

 symptom may, however, be found under other conditions (3, 9, 11, 

 13, 16, 24, 29) and is not considered characteristic of curly-top alone. 

 Very young beets may be so severely attacked that they are killed 

 before the symptoms have time to develop. 



"The serial numbers in parentheses used in this paper refer to the bibliog- 

 raphy on pp. 37-40. 

 181 



