20 



S. E. A. McCallan 



and 3 millimeters bore is very suitable. Two pieces are bent in a gradual 

 L curve. The shorter delivery piece is placed to project just below the 

 rubber stopper, while the longer piece, to which the atomizer bulb is 

 attached, is just immersed in the dust. For best results the test tube 

 should contain about an inch of dust. A separate test-tube duster 

 must be used for each dust. A thorough washing is of course essential 

 before the tube is used for another dust. If the dusters are to be used at 

 frequent intervals, the dust may safely be left in the tube. 



If consistent results are to be obtained, it is imperative that an even 

 layer of spray or dust be applied to the slides. If too much spray is 

 applied, it will tend to coalesce in large drops. A fine, even mist is the 

 most satisfactory. It is more difficult to get an even layer of dust. Large 

 particles may cause trouble, though oftentimes these may be blown off 

 without disturbing the finer dust. The tendency is to apply too much 

 rather than too little dust. In nature the average leaf seldom receives 

 a heavy coating of dust or spray. 



The general impression is that the greater quantity of fungicide used, 

 the greater is the fungicidal efficiency. Accordingly some limited tests 

 were carried out to study this point. Light, medium, and heavy applica- 

 tions of Niagara 300-mesh sulfur, Niagara Kolodust, and lime-sulfur 1:40, 

 were made. The spores used were conidia of Sclerotinia americana. The 

 results are shown in table 7. 



TABLE 7. Results of Tests to Determine the Relation between Quantity and 



Efficiency of a Fungicide 



(Percentage germination of Sclerotinia americana conidia at 24° C. in distilled water) 



* See page 21 for interpretation of letters. 



Similar results were obtained with the uredospores of Uromyces hybridii. 

 These are given in table 8. 



