April, '19] BALL: THE POTATO LEAFHOPPER 151 



were placed. The leaf hoppers on the other plants were carefully re- 

 moved before the cage was put on. The third plant remained under 

 field conditions and during the next three weeks of hot, dry weather, 

 the burning developed upon the upper part of the plant in considerable 

 amounts, so that the whole field showed a brown cast, where before it 

 had looked green. 



At the end of three weeks the cages were removed and the three 

 plants examined, after which their tops were cut off and photographed 

 and then preserved. 



The plant on which the hoppers were placed (PI. 5, fig. 1) had evi- 

 dently died within a short time, then the leafhoppers died and later, 

 two green shoots came up from the stem near the base. These were 

 green and not burned, while the former top was curled up brown and 

 dead. The check plant had grown but little in height and the burning 

 had progressed clear to the top (PI. 5, fig. 2). The plant from which 

 the leafhoppers had been removed, had grown rapidly and filled the 

 top of the cage. The leaves were broad, smooth and bright green, 

 with long, acute tips and without a trace of browning (PL 5, fig. 3). 



Is THE HOPPERBURN SPECIFIC? 



The closely related leafhoppers working on rose, apple, grapes and 

 woodbine, produce a whitened appearance on the upper side of the 

 leaves, due to innumerable minute white spots that are apparently the 

 result of feeding punctures. These feeding punctures are practically 

 all made from the under side of the leaves, where the nymphs are found. 

 In no case, however, is there any marginal burning of the leaves, or 

 any browning, until the leaves are so badly injured that they are 

 practically dead. 



In the case of the potato leaf hopper, the effect is quite different. 

 The burning occurs while the other parts of the leaf are apparently 

 uninjured and the margin of the burned area is always sharp and defi- 

 nite. This leaf hopper attacks dahlias and produces the same marginal 

 burning, as well as the same egg scars and distortion of the midribs and 

 veinlets as on potatoes. It is also found attacking water sprouts and 

 fast-growing tips of box elder trees and producing the same type of 

 burning. Water sprouts and fast-growing shoots of nursery stock, 

 and apples are also attacked, the leaves curled and the tips burned. 

 The upper leaves on fast growing raspberry canes are similarly curled 

 and burned. 



All the evidence at hand indicates that the hopperl)urn is produced 

 in every case by this one insect and by this one only. Wiietlior or not 

 it will piovc to be a specific disease like the curly-leaf, transmitted by 



