Methods in Rust Investigations 249 



but have been found very useful for separating the various cultures of 

 Puccinia triticina and other species in the study of specialized strains. 

 As the panes of glass slide up and down in a groove, plants can be re- 

 moved without lifting the cover and also various degrees of ventila- 

 tion can be employed. 



For still larger number of plants, galvanized-iron tanks, similar 

 to those described by Parker (1918), Melchers and Parker (1922) and 

 other investigators, are used. These are covered with lids in which 

 panes of glass are inset, allowing entrance of light. Wet sphagnum in 

 the bottom of the tank aids in keeping up the humidity. These tanks 

 are kept under the greenhouse bench. The floor being of cement, they 

 are easily pulled out to open and easily push back out of the way when 

 closed. 



One of the principal difficulties of successful culture in late spring, 

 summer, and early fall is the high temperature of the greenhouse. By 

 installing a system of spray nozzles beneath the greenhouse bench, the 

 tanks, belljars and plant covers are cooled by a fine spray of water. By 

 this means inoculation has been successfully cai'ried out during the hot 

 weather. When this system is used the tank covers are removed about 

 twice a day for a few minutes and the plants are thoroughly moistened 

 by leaving them exposed to the atomized spray. Thus the plants are 

 aerated and covered with a fine dew, and the humidity of the chamber 

 is renewed all in one operation. Belljars and plant covers are sprayed 

 by means of a De Vilbiss atomizer. Inoculation chambers of the iceless- 

 refrigerator type, described by Hunt (1919) also have been used in 

 greenhouses where no spray system was available, cooling being ob- 

 tained by evaporation from the wet muslin cover of the chamber. Mel- 

 hus, Dietz and Willey (1922) also have described a series of muslin 

 compartments in which their cultures are both kept and inoculated and 

 which are cooled by a fine spray of water. 



Where only one culture of a rust is being used in a greenhouse and 

 the number of plants being inoculated is very large, as in the Fj genera- 

 tion of a hybrid, the plants are dusted as described above and, after 

 atomizing, a moist chamber is created by covering the pots of plants in 

 place on the bench with heavy muslin. This is kept from resting on the 

 plants by stakes placed at intervals in the bed. The muslin is kept wet 

 by spraying as often as necessary during the day. This in reality is a 

 very flexible moist chamber. It is especially useful where the plants to 

 be inoculated are grown in soil on a greenhouse bench. In this way, 

 thousands of seedlings of corn have been inoculated, notes taken, further 

 selections of corn planted, inoculated, etc., all within a comparatively 

 short time and with much less labor than if planted in pots and inocu- 

 lated by hand. 



8, General Treatment of Cultures. Inoculated plants usually are 

 left in the moist chambers for about 48 hours. It is not advisable, when 

 removing, to place them on the greenhouse bench in direct sunlight while 

 tender from confinement in the moist chambers as the plants are likely 

 to scald. It, therefore, is best to remove them in the late afternoon. 



The incubation period of the rusts varies somewhat with the spe- 



