16 BULLETIN" 1046, U. S. DEPABTMEFT OF AGRICULTURE. 



the first year in carrying the cultures through the summer, on account 

 of the prolonged periods of temperatures ranging from 100° to 110° F. 

 It was found that sprays of water directed upon the chamber not 

 only cooled the air in the greenhouse but in addition kept the tem- 

 perature in the damp chambers within a few degrees of that of the 

 water itself. By such means a difference of 11° C. between the tem- 

 perature inside and that outside the chambers was obtained, as 

 shown by some of the readings at different dates during July and 

 August. 



Johnson (21) foimd that the maximum temperature at which ure- 

 diniospores of Puccinia graminis would germinate in a normal manner 

 was about 88° F., though the experiments of the writers have shown 

 that temperatures of 80° to 95° F. do not prevent normal infection. 

 However, temperatures of 65° to 70° F. are believed to be the most 

 favorable for inoculations with stem rust. These methods have been 

 satisfactory in every respect; 100 per cent of infection always was 

 obtained on plants of susceptible varieties, including checks, and 

 it is believed the notes on resistance or susceptibility are as depend- 

 able as can be obtained under greenhouse conditions. The methods 

 described, however, might not give as satisfactory results with other 

 cereal rusts. 



INOCULATION IN THE HEADING STAGE. 



One plant of each variety which was grown in the rust nursery was- 

 allowed to develop to the heading stage in the greenhouse. One seed 

 was sown in each pot in October. It has been found that by main- 

 taining the proper temperature, either spring or winter wheat can be 

 matured and normal seed developed in the greenhouse. Hutcheson 

 and Quantz (18) have shown that temperatures from 55° to 70° F. 

 are best suited to this purpose. In the experiments of the writers,, 

 where plants were grown to the heading stage, a night temperature of 

 about 50° F. was maintained, but not infrequently the night tempera- 

 ture during the early stages of growth fell as low as 35° or 40° F. 

 The temperature was kept below 75° F. during the daytime whenever 

 possible. 



The plants were inoculated as soon as the heads were well out of 

 the boot and the neck or peduncle exposed, as illustrated in Plate VHI. 

 Two to six culms of each variety were inoculated with stem rust. In 

 the case of Kanred, P1066, and P1068 the inocidations included a much 

 larger number of plants. In some cases the culms of these three 

 varieties were reinoculated a number of times, so as to expose them 

 to infection as often as possible and at different periods of development. 

 The uppermost leaf blade 'and the sheath of each culm of all varieties 

 grown were thoroughly inoculated, as were the necks, glumes, and 

 awns. These plants were then placed for a period of 48 to 72 hours 

 in a specially constructed galvanized-iron damp chamber, similar ta 

 the one described by Parker (34) . This damp chamber is of sufficient 



