38 



A STUDY IN CEREAL RUSTS 



servations, but there was no great difference of opinion in any case. 

 The order in which different observers placed them was sometimes dif- 

 ferent, showing that there was sometimes little choice among the 

 various pots. The results are given in the following table : 



EFFECT OF FERTILIZERS ON VIRULENCE OF RUST ATTACK 



In this experiment the two most resistant forms available for study 

 were watched very carefully. Both Kubanka 2094 and Khapli proved 

 to be very resistant even when very highly fertilized. It is a rather 

 striking fact that in both cases plants grown in sand showed a slightly 

 more virulent infection. The differences were not great. In fact, it 

 was often hard to decide which plants were most severely affected. It 

 was observed that plants which had been under the most favorable con- 

 ditions for infection were most severely attacked regardless of the fer- 

 tilizer used. The difference in conditions was due to the fact that there 

 were not enough bell jars to cover all the plants, so some were placed 

 in tubs containing water on the bottom. They were then covered with 

 pieces of glass. The films of moisture were not so persistent here as 

 under the jars, and the difference in the amount of rust was quite 

 marked. This was taken into account in determining results and mak- 

 ing comparisons. 



If these plants had been allowed to grow longer it is quite prob- 

 able that those fertilized with nitrogen would have become more se- 

 verely rusted while those fertilized with phosphorus would have been 

 slightly less severely affected. This would seem to be due not to the 

 specific action of the chemicals on the rust fungus but rather to their 

 effect on the general condition of the plant, and, in the field, on the 



