[Vol. 9 

 346 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



not being very important for this organism) were diluted with 

 sterile water before the spray was applied. (In smear inocula- 

 tions the plants were first sprayed with sterile water.) The 

 spray was obtained by using atomizers or blowers commonly 

 used by artists in "fixing" drawings. These work very rapidly 

 and effectively, producing a fine mist with little effort. 1 The 

 organism having been applied, the plants were then covered with 

 bell jars to prevent drying out. The bell jars were ensconced 

 with paper in order to cut down direct sunlight. The jars were 

 left over the plants for 1 or 2 days, depending on how high the 

 temperature happened to be. It may be worth recording that the 

 difficulty experienced in obtaining infections in the experimental 

 greenhouses of the Missouri Botanical Garden, although no such 

 difficulty had been experienced at Fayetteville, Ark., was over- 

 come by proper aeration. The greenhouse benches at the Garden 



are of concrete. When inoculated pots of plants were placed on 

 soil which filled these benches, and the bell jars which covered 

 the plants made close contact with the soil, infections were rare, 

 no matter what the temperature and humidity happened to be. 

 But by raising the jars from the soil on small blocks of wood the 

 plants were still kept moist and at the same time had access to 

 air. In this way infections were readily obtainable, other con- 

 ditions being proper. 



RELATION OF TEMPERATURE TO INFECTION 



It has already been indicated that temperature plays an impor- 

 tant role in infection. The reproduction of thermographs of 

 artificial inoculations on Winter Turf oats carried out as pre- 

 viously described, illustrates this point (fig. 1). 



The pot of plants subjected to the inoculation temperatures 

 shown in the lower graph developed no infections, while that of 

 the upper developed quite a few. It will be noted that where 

 no infections were obtained the temperature over a large part of 

 the 48-hour period was below 70° F. (21° C.), and particularly 

 during the first 24-hour period the temperature was below 70° F. 

 for 18 hours. The atmosphere was saturated and the leaves were 

 covered with water films in both cases. It was found difficult 

 to keep the incubator at an even temperature, so that no data 

 are available which will show the relationship of infection to a 

 definite temperature. Nevertheless, the graphs give some in- 



*Dr. J. A. Elliott first suggested these blowers to me. They are cheap, easily 

 sterilized, take up little space and do not plug readily. 



