RUST OF ANTIRRHINUM. 



57 



Table 10. — Effect of Various Strengths of Bordeaux Mixture 1 : 0.3 on 

 the Germination of the Urediniof-pores of P. Antirrhini. 



The urediniospores of P. Antirrhini are able to germinate in all the 

 strengths of Bordeaux mixture employed by the writer. They germinate 

 as readily in the mixture containing 1 per cent copper as in the mixture 

 containing only 0.0039 per cent copper. There was a 10 per cent difference 

 in favor of the weaker mixture, but this has no significance when we 

 consider the irregular fluctuations shown by the intermediate strengths. 

 It is probable that at the lesser strength the sprayed slide or leaf offers 

 the maximum surface of solute to the solvent. An increased strength, 

 as 1 per cent copper, means that the particles on the slide or leaf merely 

 overlap each other, and do not offer an increased surface proportional to 

 the added amount of substance. Having found a certain strength of 

 Bordeaux mixture non-toxic to the urediniospores, increasing the strength 

 of the Bordeaux mixture results in no toxic effect. 



To confirm the results of the toxicity tests of Bordeaux mixture against 

 P. Antirrhini, snapdragon plants all of the same variety were sprayed 

 with Bordeaux mixture 1 : 0.3 containing 1 per cent copper sulfate. 

 After spraying, the plants were allowed to dry, then with other plants 

 of the .same variety, not sprayed, were inoculated with snapdragon rust, 

 the urediniospores being applied to the plants in distilled water by means 

 of an atomizer. All inoculated plants, both sprayed and unsprayed, 

 were then placed for twelve hours in an incubator at a constant tempera- 

 ture of 10° C, after which they were placed together in a greenhouse 

 under the same conditions. Fifteen days after inoculation all the plants 

 which had been inoculated were examined and the uredinia on the leaves 

 were counted. The sprayed plants showed on the average two hundred 

 uredinia each, while the unsprayed plants showed on the average two 

 hundred and ten uredinia each; that is, there was an approximately 

 equal amount of infection on the sprayed and unsprayed plants. Bor- 



