RUST-RESISTANT VARIETIES OF WHEAT 39 



immediate atmospheric conditions. The direct effect of chemicals in 

 the soil on the amount of rust on resistant varieties is not great, only a 

 slight quantitative difference being apparent. 



In order to determine by more accurate methods whether or not 

 there was a direct effect of substances in the soil on the amount of 

 rust (1) fungicides were put into nutrient media, and (2) certain 

 nutrient salts were used in amounts varying from deficiency to excess. 



Sach's modified culture solution was used and to this one per cent 

 of agar was added. The series was arranged as follows, the amounts 

 of nitrate and phosphate being the variables : 



I. Potassium nitrate; 2 grams per 1,000 cc. 

 II. Calcium phosphate; 3 grams per 1,000 cc. 



III. Potassium nitrate ; .05 grams per 1,000 cc. 



IV. Calcium phosphate; .075 grams per 1,000 cc. 

 Minnesota No. 163 wheat was used. After inoculation plants were 



all placed under bell jars and kept under uniform conditions. Arranged 

 according to virulence, the most severely affected being placed first, 

 they would be arranged as follows: III, II, IV, I. 



This was tried a second time with exactly the same results. The 

 plants appeared about the same, all growing fairly well in the agar. 

 All were well infected, producing a fairly large number of large, 

 healthy pustules. They were kept three weeks after inoculation and 

 by this time there was not much difference between II, IV, and I, but 

 III was still much more virulently attacked. It seems, therefore, that 

 an excess of nitrogen does not necessarily, in itself, cause an increase in 

 the amount of rust and an excess of phosphorus does not affect it very 

 appreciably. 



The effect of excluding nitrogen and phosphorus was next tried. 

 Sach's modified medium plus one per cent of agar was again used and 

 in I no potassium nitrate was added while calcium phosphate was ex- 

 cluded from II. The plants in I were lighter colored from the first 

 than either those in II or the checks. They were inoculated six days 

 after planting. A good, vigorous infection resulted, the plants in I 

 being slightly more severely attacked than those in II. The leaves of 

 I began to turn yellow after three weeks, and the rust did not spread 

 farther. The check plants were more severely attacked than those in 

 either I or II. Here again, however, the differences were not very 

 great. There was a slight quantitative difference but qualitatively there 

 was scarcely any difference. This is in keeping with Ward's conclu- 

 sions reached after his work on mineral starvation, reference to which 

 has already been made. 



An attempt was then made to determine whether it was possible 

 to confer immunity by means of various salts. Copper sulfate, copper 

 carbonate and iron sulfate were used in strengths varying from 1 to 



