BULLETIN 629, U. S. DEPARTMENT OF AGEICULTUEE. 



them on the previously moistened leaf to be inoculated. When all 

 leaves in a pot were inoculated they were sprayed at once with an 

 atomizer and placed in the moist chamber shown in figure 1, where 

 they were allowed to remain 48 hours. These moist chambers, which 

 will hold about forty 4-inch pots, cost less than $10 for four. No 

 trouble was experienced from the leaves burning or turning yellow, 

 and almost 100 per cent of the inoculations were successful. 



Inoculations of older plants were made in the order of heading 

 of the varieties, beginning on April 10 and continuing to May 9, 

 1916. There were 12 to 18 plants in each series. The stem-rust 



spores were alwaj^s placed 

 on the sheath inclosing the 

 emerging panicle, while 

 the inoculations with 

 crown rust were made on 

 the uppermost leaf blade. 

 As with the seedlings, the 

 inoculated plants were 

 sprayed with an atomizer 

 to insure the presence of a 

 film of water and then 

 kept in the moist chamber 

 for two * days. A special 

 large glass-topped galvan- 

 ized-iron moist chamber 

 was made, holding eight- 

 een 5-inch pots and allow- 

 ing the tallest plants to re- 

 main upright (fig. 2). 



The incubation period 

 for the two rusts was ap- 

 proximately the same. 

 Generally, though not al- 

 ways, the uredinia of the 

 stem rust appeared first. Cool temperatures seemed to lengthen the 

 incubation period, for during November the house was cooler than 

 during the succeeding months and the uredinia during this time were 

 noticeably slower in appearing. Other factors, such as light, also 

 may have affected the results. 



Notes on the appearance of flecks usually were made in 7 to 9 days, 

 and those on the formation of uredinia after a period of not longer 

 than 12 days. Further notes usually were taken on the quantity and 

 character of infection. No counts of uredinia were made ; nor should 

 too much emphasis be placed on whether or not all the leaves inocu- 

 lated were equally infected, for it is obviously impossible to be cer- 



Fig. 2, 



-Glass-topped galvanized-iron moist cham- 

 ber used for mature plants. 





