1913.] PUBLIC DOCUMENT — No. 31. 169 



seed corn from wircwornis have been continued, and an improve- 

 ment on those previously discovered is now under consideration 

 for next season. 



Under the Adams fund the two projects mentioned in former 

 reports have been carried farther. The causes of the burning 

 of foliage by arsenical poisons have been given much study, ac- 

 companied by over a thousand separate field tests, each followed 

 by an examination of the results of the treatment at intervals 

 of a day or two for more than a month. Closely involved in 

 this has been the consideration of the nature of the insecticides 

 used, and in this portion of the work the co-operation of the 

 chemical department of the station has been invaluable. 



If the causes of injury to foliage following the application 

 of arsenicals are to be clearly understood, it is evident that the 

 composition of the materials applied must be known. The in- 

 jury may in fact be due, either to impurities in the materials 

 themselves, to their decomposition after application to the leaves, 

 or to something normally and necessarily present in them. To 

 avoid the first possibility, materials as nearly absolutely pure 

 as it is possible to obtain have been sought, and have only been 

 found after many trials, it being evident that almost none of 

 the insecticides on the market at the present time are pure or 

 even an^-where near it. As it is quite possible that the impuri- 

 ties are the cause of the injuries, it is of course desirable to 

 eliminate these, and in the materials used the first season it 

 Avas supposed that this had been accomplished. Too late it was 

 learned that this was not the case, and that the treatment was 

 made with substances which had been guaranteed pure by the 

 manufacturers, but which were far from being so. The conse- 

 quence was that the chemical department was obliged to take 

 up the problem of finding methods by which pure Paris green, 

 arsenate of lead and arsenate of lime could be made, and of pro- 

 viding this department with them in quantities sufficient for use. 

 This has been successfully accomplished, and the spraying last 

 year, in part, and th^ past summer has been with these. 



The actual value of wasps as parasites has never been investi- 

 gnted carefully. General statements that they are " extremely 

 useful," or that " their importance can hardly be overestimated," 



