294 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



crushing of the insects apparently fails to dissolve enough of this toxic 

 substance to produce injury in all cases. 



Experiments with Potometer 



It was thought that it might be possible to get more of the leafhooper 

 solution into the leaves by cutting them off and placing the stems in the 

 solution so that it would be drawn up into the leaf by transpiration. 

 Accordingly, a number of hollow glass tubes were bent into a "U" shape, a 

 rubber tube was placed securely over one end of the glass tube and then 

 into this rubber tube the stem of an entire leaf was firmly placed and held 

 there by grafting wax. After trying this out and finding that most of the 

 leaves remained fresh for some time under these conditions with water in 

 the tube, a solution made from 50 crushed nymphs was poured into 

 one of the tubes. The diameter of the tube was so small that it was 

 possible to fill it with a highly concentrated extract. As this was 

 darker colored than the water it could be easily seen that the extract 

 was being drawn up into the leaf which promptly became flaccid and 

 remained so without entirely wilting for five days. At the end of five 

 days, on August 29, the leaf was removed. It had yellowed in certain 

 areas, and there had been a tendency for the margin to roll up, a con- 

 dition similar to the beginning of hopperburn. It was found that the 

 cut end of the stem had partially decayed, a condition brought about 

 by the fermentation of the insect remains in the water. The decayed 

 part was cut off and the leaf placed with the stem in water. It soon 

 freshened up and August 31 the leaf had recovered except in the in- 

 jured portion. The injury resembled hopperburn very closely. Leaves 

 in plain water remained perfectly fresh and showed no injury 

 throughout this test, provided the apparatus was "working properly. 

 This experiment was repeated later with the difference that only the 

 clear solution free from the insect remains was used, thus avoiding 

 decay of the leaf due to fermentation. The leaf became flaccid as 

 in the other case and then developed s^nnptoms of hopperburn. 



Discussion of Inoculation Results 



The writers were at a loss at first to understand the variable results in 

 the different inoculation tests with hypodermic needles as described in the 

 preceding paragraphs. It was noted, for example, that extracts from 

 crushed adults caused marked symptoms of hopperburn in one series of 

 inoculations and negative results in another. Furthermore, it was noted 

 that extract from crushed nymphs produced less abnormalities in the leaf 

 tissue than from the macerated adults. This would indicate that 



