April, '21] GiDDiNGS: dusting vs. spraying 229 



What is the effect of sunlight ? 

 What is the effect of heat ? 



What is the effect of diurnal temperature variation? 

 What is the effect of moisture ? 



What is the combined effect of moisture and temperature vari- 

 ations ? 



Is there any consistent and pronounced difference in the action of this 

 material upon different varieties or species of plant, and if so why? 



Perhaps some of you are now convinced that the dusting problem 

 has been too great a strain upon me, but let me assure you in all serious- 

 ness that our progress in phytopathology will eventually be based upon 

 the correct answers to such fundamental questions. A reasonable 

 knowledge regarding these factors will save many disputes and mis- 

 understandings, and will explain m^any of those things which we, "are 

 sure cannot be so," but which are so. 



The abo\'e-mentioned questions must also be applied to dust com- 

 binations such as the sulphur- arsenate, copper-lime-arsenate, sulphur- 

 lime sulphur-arsenate, and others. As already indicated, there are 

 numerous other materials or combinations of materials which are worthy 

 of consideration, and possibly of trial. 



Methods of treatment and methods of handling results are also worthy 

 of study. This is a field in which we should be able to agree to a reason- 

 able extent. There has undoubtedly been a considerable and steady 

 improvement in methods, but it must continue. New developments 

 in equipment and materials will also have their effect upon methods of 

 treatment. 



There is a vast amount of work to be done. The field is large and no 

 one institution will be likely to solve many of the problems involved. 

 By reasonable co- operation the progress will be more rapid, but we will 

 need abundant help from chemistry and physiology. In this case our 

 problem is also the ijroblem of entomology and horticulture and we 

 know that their co-operation is assured. 



There is a strong natural tendency to publish positive results and to 

 avoid the publication of negative results. This is an unfortunate trait, 

 for the negative data from, a good investigation, well conducted, are 

 of greater actual value than j^ositive data from a similar investigation 

 poorly conducted. 



I believe that all of us should submit the results of our investigations 

 to disinterested, but cayjable, parties who will give them their frank and 

 careful criticism before we turn them over to the printer. I am certain 

 that such action wcjuld prevent many unintentionally misleading 

 statements which find their way into print. 



