58 MASS. EXPERIMENT STATION BULLETIN 202. 



deaux mixture cannot, therefore, be recommended for the control of 

 snapdragon rust. Peltier (1919) also came to the conclusion that Bor- 

 deaux mixture 4-4-50 will not control snapdragon rust. 



Continuing the study of the toxicity of Bordeaux mixture to members 

 of the Uredinales, the writer tested the effect of this fungicide on the 

 germination of the urediniospores of carnation rust, U. CaryophylHnus 

 (Schrank) Wint. It is realized that growers do not often spray for carna- 

 tion rust now, being able to control this disease by cultural methods 

 and varietal selection. But Bordeaux mixture has often been recom- 

 mended for the control of this rust. Bordeaux mixture 1 : 0.3 was used 

 in these tests in various strengths, so as to contain 0.5, 1, 2 and 4 per cent 

 copper sulfate. The method employed was the same as that described 

 for P. Antirrhinl, except that the spores were germinated at 14° C, which 

 temperature was found by the writer (Doran, 1919) to be the optimum 

 temperature of germination for the urediniospores of U. CaryophylHmis. 

 These urediniospores, like those of P. Antirrhini, germinated only when 

 in contact with both air and water, spores in the interior of the drop 

 of water never germinating. 



The toxicity tests conducted by the writer showed that Bordeaux 

 mixture is not toxic to the urediniospores of U. CaryophylHnus, which 

 indicates that the behavior of the urediniospores of P. Antirrhini toward 

 this fungicide is not exceptional. If carnation plants sprayed with Bor- 

 deaux mixture failed to rust, it must have been due to other adverse 

 conditions, such as temperature, which prevented spore germination and 

 infection. 



It would appear from data obtained by others as well as from the 

 results here reported that the Uredinales are much more tolerant of 

 copper than are the Phycomycetes. Melhus {loc. cit.) found Bordeaux 

 mixture toxic to Phytophthora infestans (Mont.) De Bary at 0.0039 per 

 cent copper sulfate. But the writer did not find Bordeaux mixture toxic 

 to the two members of the Uredinales studied at 4 per cent copper sul- 

 fate. It may be that the thick wall of the spore secretes some chemical 

 substance which prevents the copper in the Bordeaux mixture from going 

 into solution. 



The literature contains numerous references to the use of copper solu- 

 tions as a control of diseases produced by members of the Uredinales, 

 but there is a variance of opinion as to the effectiveness of copper on 

 rust diseases. 



The experiments performed by earlier investigators were mostly of the 

 field rather than the laboratory type. Dudley (1890) recommended a 

 saturated solution of potassium permanganate as a control of hollyhock 

 rust. Maynard (1893) found Bordeaux mixture to give good results 

 as a control of carnation rust. Hitchcock and Carleton (1893) found 

 the spores of P. graminis Pers. able to germinate in solutions of thirty 

 chemical compounds of various strengths, including 0.1 per cent solutions 

 of mercuric chloride, copper acetate, potassium bichromate, potassium 



