28 THE CURLY-TOP OF BEETS. 



of curly-top the following spring if the beet is planted for seed pur- 

 poses. 



Of seed beets the writer could never observe that plants as a whole 

 ever succumb to the attacks of the leafhoppers during the season they 

 are planted as seed beets. They are too vigorous and resistant, and 

 nearly all the leaves are full grown before beet leafhoppers appear 

 in number. However, individual shoots and racemes put forth late 

 in the season may manifest the symptoms if attacked by leafhoppers 

 (fig. 8). Then, too, the entire aftergrowth, which generally develops 

 late in the summer, after the seed has been harvested, may exhibit 

 pronounced signs of the disease. This actually occurred on the plat 

 at Garland after the seed harvest of 1908, when the aftergrowth of 

 nearly every seed beet became thus affected. This aftergrowth con- 

 sisted of actively growing and immature leaves in which cell division 

 w T as taking place. 



The symptoms are generally more diverse in seed beets. Appar- 

 ently the element of greater resistance on account of greater size and 

 vigor is a factor tending to the production of symptoms not com- 

 monly noted in young sugar beets. However, these additional, and 

 among sugar beets less usual, symptoms may be seen in sugar beets 

 when quite largo plants are attacked by so many leafhoppers that 

 even they finally succumb. These symptoms are those mentioned as 

 the retracted type. 



The writer has been able to produce the retracted curl under test 

 conditions by imprisoning a gradually increasing number of leaf- 

 hoppers with beets that would ordinarily fail to develop the symp- 

 toms on account of their size when attacked by the insects (see figs. '1 

 and 3). 



SEVERAL TYPES OF LEAF-CURL ON SEED AND SUGAR BEETS. 



As a result of observations on the development of the disease in 

 seed beets the w T riter has been able to note several types of symptoms 

 on them, as follows: 



(1) The type most commonly noted on sugar beets and hitherto 

 regarded as the characteristic appearance of beets affected with curly- 

 top, viz, with leaves strongly curled inward from the entire margin 

 toward the midrib; strongly knotted veins; thickened parenchyma, 

 which in advanced stages is quite brittle, though tough and leathery 

 in appearance; very dark and dull green foliage with outer whorls 

 sear and dead; pronounced inhibition of growth; early appearance of 

 feeble seed stem, which sometimes does and sometimes does not mature 

 seed. (See PI. I, fig. 1; PI. II, fig. 1; PI. IV, fig. 1; PI. VI, fig. 1; 

 and PI. IX, 'fig. 1.) 



181 



