Studies on Fungicides — III 37 



hypha tips of many parasitic fungi, especially when they come into contact with a solid 

 body and in case the solid particle contains copper, might dissolve a considerable amount 

 just about the delicate growing tip. 



If, as is quite possible, the copper is quickly absorbed by the fungous cells, .the solvent 

 could then take up another portion, which in turn would be absorbsd by the fungus, and 

 so on. In this manner poisoning might ensue, even though the copper were only very slightly 

 soluble. 



Frank and Kruger (1894) found that spores of different Peronosporaceae 

 and other fungi were killed when immersed for 24 hours in bordeaux 

 mixture several weeks old. However, when similarly treated with the 

 nitrate from the mixture, they were not killed, but germinated. The 

 filtrate showed no soluble copper by chemical tests, and these authors 

 conclude that the presence of the insoluble copper is necessary to bring 

 about the death of the spores. 



Rumm (1895) placed uredospores of Puccinia coronata in drops of 

 bordeaux mixture. Those spores not in contact with the bordeaux par- 

 ticles, not only were not injured, but germinated. Only when the spores 

 were in contact with the particles or immediately over them, were they 

 killed. As a result of this test, Rumm believes that bordeaux mixture 

 is not fungicidally active at a distance from the particles. However, 

 Doran (1923), as well as workers in the Cornell laboratory, have found 

 that the uredospores of grain rusts are not very sensitive to the toxic 

 action of copper fungicides. 



Aderhold (1899) obtained some interesting results while studying the 

 poisonous action of bordeaux mixture. He found that spores of 

 Fusicladiwn pirinum would germinate on the surface of pear leaves 

 sprayed with bordeaux mixture, provided the spores were between the 

 flecks of bordeaux, but that there was no germination directly over the 

 flecks. Also, the spores would germinate in drops of rain water collected 

 from leaves that had been sprayed. Drops of bordeaux mixture were 

 dried down, and strips of filter paper, moistened with rain water and bear- 

 ing spores of Fusicladium, were placed with one end on the dried bordeaux 

 drops. At a distance of to 4 millimeters from the bordeaux drop, no 

 germination occurred. Progressing farther away from the bordeaux, the 

 germination improved, and at 10 to 13 millimeters distant it was normal. 

 Aderhold believes that the fungicidal action is in evidence only during 

 the formation of the germ tube or during invasion itself. 



Clark (1902:41) appears to have followed Swingle's suggestion with 

 an experiment. Spores of various fungi were placed in a mixture of 

 copper hydroxide and water in which no soluble copper could be detected 

 beforehand. The spores were killed in a short time, and traces of copper 

 were found in the suspension, thus " showing that they dissolve more of 

 the Cu(OH) 2 than was required to kill them" (page 42 of reference cited). 

 No controls are mentioned. Clark found further that thin-walled spores, 



