232 NINETEENTH REPORT. 



The figure known as the copper sulphate coefficient given in the tables 

 represents the relative spore killing povi^er of a given fungicide as com- 

 pared with that of a known strength of copper sulphate in the same 

 periods of time and under exactly the same conditions. In the calcula- 

 tion of this coefficient, tlie Anderson and McClintic method is used. The 

 copper sulphate coefficient is arrived at by dividing the figure represent- 

 ing the degree of dilution of the weakest strength of the fungicide used 

 that kills within five minutes by the figure representing the degree of 

 dilution of the weakest strength of the copper sulphate solution which 

 kills within the same time. The same is done for the weakest strength 

 that kills within 45 minutes. The mean of the two is the coefficient. 



In the work with lime sulphur compounds the dilutions were so great 

 that variable results occurred. These results were probably dependent 

 upon obscure chemical changes that took place at this dilution. For 

 this reason the coefficient of lime sulphur is likely to be more or less 

 variable even when the same standards are used in the experiment. 

 These differences, however, are not so great but that the coefficients are 

 of some value in comparing with each other the various commercial 

 mixtures of lime sulphur. 



Two copper fungicides, ammoniacal copper carbonate and neutral 

 coj^per acetate were tested, and coefficients determined. The results and 

 coefficients obtained are shown in Table No. 5. 



The copper fungicides showed much less variations in their action than 

 was the case with lime sulphur preparations. This was undoubtedly due, 

 at least in part, to the fact that both ammoniacal copper carbonate and 

 neutral copper acetate are relatively stable compounds, and for that 

 reason not subject to the great variation in dilution that was exhibited 

 by the lime sulphur preparations. The coefficient really indicates the 

 difference in toxic effect of different copper compounds. The fact that 

 ammoniacal copper carbonate gives a positive coefficient of three may be 

 due to some extent to the free ammonia present in the dilutions. But 

 for the fact that the solution was made so strong, a fractional coefficient 

 might have been calculated as was the case with neutral copper acetate. 



Wlien E. parasitica was substituted for G. rufomaculans as tlie test 

 organism several rather unlooked-for facts were brought out. The 

 spores of this organism proved highly susceptible to the lime sulphur 

 mixtures, but on the other hand were extremely resistant to the action 

 of the copper sulphate standard. It will be seen from Table No. 6 that 

 the dilutions of the one to forty standard run from 1-300 up to 1 to 600. 

 On the other hand a 20% solution of copper sulphate had to be sub- 

 stituted for the 10% solution used with G. rufomaculans and even then 

 the killing point in the five-minute period was at the 1-1 dilution. These 



