266 Journal of Agricultural Research voLxix.no. 6 



Hayman {12) repeated his experiments for five years and grew 195 

 plants to maturity. The conditions inside his cages were abnormal at 

 all times, although an effort was made to control conditions by means 

 of a blacksmith bellows and cotton filters. Two pustules of rust ap- 

 peared in the fifth year, but the author himself was not satisfied with 

 this result as is evidenced by the fact that he states that the tar used to 

 coat the inside of the cages had oozed through the cracks in the cage in 

 which the plant was found to be infected. 



Massee, the only other worker who secured positive results, used bell 

 jars placed upon cotton wool with a cotton plug in the opening at the 

 top. He sowed wheat inside these jars, which was known to be shriv- 

 eled by Puccinia glumarum, and as controls he sowed plump seed of 

 the same variety. Sixty per cent of the infected seed germinated, and 

 when the plants were 3 inches high rust appeared in each pot. When 

 the plants were 5 inches high 26 per cent of them were rusted. Of the 

 plump seed sown under the same conditions 96 per cent germinated, and 

 all remained perfectly free from rust. These results are striking, and 

 the problem with this rust is highly deserving of further investigation. 



Pritchard {21) grew 60 wheat plants from rusted seed in glass cages in 

 the open and later repeated the experiment in the greenhouse. No 

 rust appeared on any of the plants. He states that the plants headed 

 and blossomed but no kernels developed because the temperature and 

 moisture conditions were abnormal. He also refers to an experiment 

 where wheat sown at different dates was inoculated with both aeciospores 

 and urediniospores of stemrust. Rust did not appear abundantly, 

 however, until the wheat began to head, when each sowing became 

 thoroughly rusted. He states that it is possible to attribute this pecu- 

 liar behavior to infection through the seed with a long subsequent incuba- 

 tion period in the growing plant. It seems to the writer that this con- 

 clusion is entirely unwarranted, since it is well known that infection 

 with stemrust is much more easily obtained and more noticeable during 

 the heading period of the plant when stemrust does such great damage 

 by attacking the neck of the stalk. This is a period of rapid growth of 

 the plant and a period when urediniospores are usually present in abund- 

 ance in the air. If climatological conditions are favorable — that is, if 

 high relative humidity and comparatively low temperatures prevail dur- 

 ing this period — a severe rust epidemic is almost sure to follow if the 

 infection material is present. A study of the climatological conditions 

 during the last of June and the first of July in the spring-wheat belt 

 shows that these conditions existed in the years when rust epidemics 

 were severe and did not exist in the years when rust was not prevalent. 

 These conditions are sufficient to explain any such peculiar behavior as 

 Pritchard refers to and also help to explain rust epidemics in the spring- 

 wheat region. 



