234 NINETEENTH REPORT. 



The coefficient shown above are lower with E. parasitica than with G. 

 rufomaculans. In the case of the Ammoniacal copper carbonate the 

 coefficient is 3, witli E. parasitica it is 1.75. G. rufomaculans used as the 

 test organism with neutral copper acetate gives a coefficient of .7 but 

 with E. parasitica the figure is .30. When the increased strength of the 

 copper sulphate standard (from 10%> to 20%) is taken into considera- 

 tion the discrepancy is wholly eliminated and it is seen that a coefficient 

 is equivalent to a coefficient of .7 with a 10% solution. Yet in spite of 

 this, repeated trials with a copper sulphate solution of 10% showed 

 conclusively that it was not sufficiently strong to kill the spores even at a 

 1-1 dilution whicli was the strongest available under the conditions of the 

 method of procedure used. These facts point to the conclusion that 

 neutral copper acetate is more toxic to the spores of E. parasitica than is 

 copper sulphate. 



The coefficients that have been determined in this paper represent a 

 general comparison of the various mixtures of lime sulphur and of the 

 two copper compounds used, with a copper sulphate solution of a standard 

 strength. The figure representing the coefficient has no value except for 

 comparison. The coefficient must be carefully interpreted because of the 

 unequal proportion in which the dilutions of the standard solution and the 

 fungicide are made up. For example^ the experiments with lime sulphur 

 show a difference in dilution of 20 when dilutions are 1-220, 1-240, etc. 

 The killing point of lime sulphur therefore is determined with an accuracy 

 of 2~2~o or iV. On the other hand the dilutions of copper sulphate are 

 1-5, 1-10, etc. In this the point that permits growth is one-half weaker 

 than the dilution that kills. The rate of increase in dilutions should be 

 as near the same with both trial fungicide and standard solution as 

 possible. It would be desirable to increase tlie dilution of copper sulphate 

 by one instead of five and so determine more accurately the killing point 

 with this material. The mathematical calculation of the coefficient would 

 thus be more exact. 



The method here recorded has proved less, satisfactory for the lime 

 sulphur mixture than for the copper compounds. In some cases the 

 results obtained with lime sulphur showed slight variation. This was 

 especially true when very dilute solutions were used such as was neces- 

 sary when E. parasitica was the test organism. In such cases many trials 

 were made and the average taken. The copper solutions did not sliow 

 such variations. 



Of the organism used G. rufomaculans seemed to be best suited for a 

 standard although the possibilities of biological strains is an important 

 drawback in its use. The variability in spore resistance exliibited by E. 

 parasitica, especially with lime sulphur, makes it of little value as a test 



