648 



STATE BOARD OF AGRICULTURE. 



concerning 



this burning as is sliown by the work of Martin^, Diig- 

 gar and Cooler'', and Lutnian'*. who in studying the effect of bordeaux 

 mixture found that tlie transpiration was greater in sprayed than in 

 unsprayed plants. Another seeming inconsistency of the dry weather 

 theory is found in the Colorado potato regions, where hot, dry weather 

 with very brilliant sunshine is the usual occurrence and where '*tip- 

 burn'' is very rare. 



The leaf hopper as a causal factor: A more satisfactory explanation of 

 the cause of tipburn and one which eliminated the vagueness embodied 

 in weather effect was offered by BalF in 1918. He attributed the injury 

 to the leaf hopper, Empoasca mail LeB, having arrived at his conclusion 

 after conducting two cage experiments during one growing season. 

 Ball's findings, hoAvever, were so revolutionary in addition to being 

 based upon rather meager experimental data, although well supported 

 by a large amount of field observations, that entomologists and plant 

 pathologists were slow to accept this explanation of the cause of tip- 

 burn. The disease being of such significance in Michigan investigations 

 of the cause of the burning of potato foliage were undertaken at the 

 suggestion of G, H. Coons and field experiments Avith caged plants in 

 the summer of 1919 and greenhouse experiments in the fall of 1919 were 

 undertakeu which gave convincing information of the correctness of 

 Balls findings (Kotila"*). These experiments, as well as those of two 

 other seasons are detailed below. 



EXPERI MENTATION 



Field experiments were conducted during the 1919, 1920, and 1921 

 growing seasons at the Upper Peninsula Experiment Station at Chat- 

 ham, Michigan, in which insect tight cages (Fig. 2) of sutficient size to 



Fig 2. Type of cages used in field experiments. 



