308 Agricultural Experiment Station, Ithaca, N. Y. 



statements do not exaggerate the matter, for the vigor of the 

 entire plant is frequently much reduced by these insects. 



From what has already been said regarding the physiological 

 effect of other injurious influences, it would seem very probable 

 that the work of the flea-beetle may also be considered as being a 

 means of reducing potato plants to a condition which renders the 

 development of the early blight fungus possible. This supposi- 

 tion is supported by facts. If a potato leaf is examined when the 

 first traces of early blight appear, it will probably be found that 

 the first browning of the tissue occurs about the edges of holes 

 made by flea-beetles, or in places in which the tissues have been 

 but partially injured. This is perhaps not always the case, but 

 it has proved to be so in the vast majority of the leaves which I 

 have examined. A reddish-brown zone of varying width is 

 formed about a central point (see plate) and this gradually 

 enlarges until other similar discolorations are met, and the grad- 

 ual uniting of several of these originally distinct areas, causes the 

 more or less continuous destruction of the tissues at the edges of 

 the leaflets. When the discolorations start nearer the center of 

 the leaf, they generally remain isolated for a longer period. 



The later stages of the disease are well known to potato grow- 

 ers. The entire leaves graduallj^ assume the brown and shrivelled 

 appearance, and the stems in turn become yellow, dry and brown, 

 so that nothing remains of a formerly green and flourishing plant 

 except a few withered remnants of foliage and a number of small, 

 partially developed tubers. These do not rot, but owing to the 

 death of the tops they remain small from want of nourishment. 



It follows from the preceding remarks on the early blight, that 

 the fungus which is commonly held responsible for the injurj^ is 

 not a true parasite; that is, it will not attack healthy tissue, but 

 only succeeds in obtaining a foothold after the potato foliage has 

 become weakened by age, by unfavorable climatic conditions, or 

 by mechanical injuries chief among which is probably the flea- 

 beetle. This places the most effective lines of treatment upon a 

 different basis from that generally followed with other fungous 

 diseases; instead of preventing the entrance of the organism by 

 means of protective substances, the constitution of the plant 



