Yo 
16 BULLETIN 1046, U. S. DEPARTMENT 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) found 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 (1/8) 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 VIII. - 
‘Two to six culms of each variety were inoculated with stem rust. In 
the case of Kanred, P1066, and P1068 the inoculations 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 to. 
the one described by Parker (34). This damp chamber is of sufficient. 
