54 



MASS. EXPERIMENT STATION BULLETIN 202. 



were removed from living leaves by means of a stream of water from a 

 pipette. These spores were shaken up in distilled water, drops of which 

 were then placed on the spraj-ed and dried slides, and also on other un- 

 sprayed slides used as checks. This gives conditions similar to those 

 the spores meet on spraj^ed and unsprayed leaves. The slides bearing 

 the spores were then placed on culture plate benches in moist chambers, 

 and these were placed at 10° C, the optimum temperature for the germi- 

 nation of urediniospores of P. Antirrhini. Here they remained for at 

 least twelve hours, when the drops were examined microscopically, the 

 spores counted, and the percentages of spores germinating determined. 

 If there was no germination on the check (unspraj^ed) slides the results 

 on the sprayed slides were of course discarded. At least three tests 

 were made with each strength of solution. Only dilutions near the 

 limit of toxicity are given in the tables, although stronger and weaker 

 solutions were also used. 



Copper sulfate was tested in dilutions ranging from .0039 to .25 per 

 cent copper. The toxicity of copper sulfate is shown in the following 

 table : ■ — 



Table 6. — Effect of Various Stre7igths of Copper Sulfate on the Germi- 

 nntion of Urediniospores of P. Antirrhini. 



It is thus seen that copper sulfate prevents germination of the uredin- 

 iospores of P. Antirrhini at a strength of solution of 0.25 per cent copper. 

 Melhus (1915) found copper sulfate toxic to the spores of Phytophthora 

 infcstans (Mont.) DeBary when the solution contained .0157 per cent 

 copper. The indications are that the Uredinales are much more resistant 

 to copper than arc the Phycomycetes. 



To determine the toxicity of copper sulfate to foliage of snapdragon, 

 plants were sprayed with copper sulfate solutions containing from 0.25 

 to .0312 per cent copper. The sprayed plants were then dried slowly; 

 that is, they were allowed to remain six hours in a moist chamber after 

 spraying. The results are given in the following table: — 



