290 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



characteristics are the deep brown color of the burned areas, the curling 

 upward and rolling in of the leaf margin and the crisp, fragile nature 

 of the dead tissue. Tipbum as characterized by Lutman (Fig. 15, 5) 

 has no relation to the venation, a fact which distinguishes it at once 

 from hopperburn. The writers are not familiar with this type of 

 burning which apparently is not common in Iowa. Bum injury (Fig. 15, 6) 

 is rarely seen in the field but can be produced experimentally by 

 placing leaves near intense heat. The burned areas in this case al- 

 ways run between the larger veins, the tissue immediately surrounding 

 these being the last to die. vSun-scald (Fig. 15, 7) is fairly common in 

 Iowa but is not serious. It is noticed usually before the first signs 

 of hopperburn appear and is the result of the action of the sun's rays 

 through drops of water resting on leaves after a rain. These drops 

 of water, if they are not evaporated or blown from the leaf soon, act 

 as minute burning glasses and the tissue beneath bums brown. This in- 

 jury is not correlated with veins or margins. The leaf is also dis- 

 torted in the affected region by being folded. Another type of injury 

 (Fig. 15, 8) is commonly seen on potato leaves in greenhouses. It re- 

 sembles hopperburn in that it is correlated with the veins and begins at 

 the margin and it also often appears on the lower and older leaves of 

 the plant. It is distinct from hopperburn, however, in that the tissue 

 only turns a comparatively light brown, there is little or no curling 

 upward and rolling in of the leaf, and the burned area is more or less 

 leathery in texture. Leaves affected with this disease appear limp and 

 wilted. This is discussed in more detail in the following paragraphs. 



Effect of Mutilation of the Potato Leaves 



Preliminary experiments on the effect of mutilation of potato leaves 

 have already been mentioned.' This year these tests were repeated, using 

 sterilized as well as non-sterilized instruments. The first series of tests 

 consisted in pricking the larger veins with minuten Nadeln, once or several 

 times both before and after these were sterihzed. Seven days later the 

 first signs of burning were noticed on several of the leaves so treated. 

 This appeared in the fonn of a very small triangular brown area at 

 the tip of the leaf and developed regardless of whether a sterilized or 

 non-sterilized needle had been used. On the fifteenth day after the 

 veins had been pierced all of the leaves but one showed this same type 

 of injury. 



Other leaves were similarly treated, using instead of the needles 

 the fine, sharp ovipositors of two species of parasitic Hymenoptera. 



iPenton, F. A. Journal of Economic Entomology, Vol. 14, No. 1, pages 71-72, 

 1921. 



