August, '22] FENTON & RESSLER: ARTIFICIAL PRODUCTION OF HOPPERBURN 291 



Of the two types of ovipositors used, one, the larger of the two, was 

 comparatively short and stout, while the other was longer, finer and 

 more flexible. These were used both before and after being sterilized. 

 After 15 days a small burned area appeared at the tips of som.e of the 

 leaves but several remained normal. 



Finally, several leaves were mutilated by severing one or more of 

 the larger veins and the midrib with a scalpel both before and after 

 sterilizing the instrument. Seven days after this test a small dead 

 area was noticed on one of the leaves mutilated in this manner, but 

 this did not increase noticeably after this date. 



Discussion of Mutilaton Experiments 

 In the above experiments it was noticed that the first signs of burning 

 appeared suddenly on different plants on the same day. Possibly some 

 abnormal change in temperature or hiunidity occurred on this date which 

 was the real cause of the sudden appearance of burning. The fact that 

 some check leaves showed this type of injury seems to substantiate this 

 conclusion. Furthermore, the burned areas on the mutilated leaves were 

 very small, and not at all similar to hopperbum. They did not enlarge in 

 size nor were they preceded by any yellowing of the tissue, loss of tur- 

 gidity, or curling upwards of the leaf as always accompanies typical 

 hopperburn. The writers have repeatedly observed similar small 

 brown areas on leaves that were not mutilated in any way and believe 

 that under the abnormal conditions which are present in the green- 

 house, the older leaves on a plant are very apt to show these areas. 

 They feel therefore that they have not succeeded in producing anything 

 which is at all comparable to hopperbum by mutilation of the leaves 

 and that it is certainly not produced by the mere mechanical injury 

 following feeding or oviposition by the leafhopper. 



Effect of Dilute Poisons on Potato Leaves 

 Potato leaves were injected with five per cent hydrochloric acid and 

 others with five per cent ammonium hydroxide by means of a hypodermic 

 needle. Within 24 hours these leaves were wilted and shrivelled but there 

 was no sign of burning. After this the leaves dried and the dead areas 

 gradually turned a light brown color but the injury was in no way 

 similar to hopperbum. Check leaves inoculated with water blanks 

 remained normal. 



Inoculation of Hopperburn Tissue Solution into 

 Potato Leaves 

 On July IS a small amount of solution prepared from a 

 macerated potato leaf showing a trace of hopperbum was injected 



