562 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
an extremely susceptible variety of wheat, Haynes Bluestem (Minne¬ 
sota No. 169), was used as the host plant. Figures ii and 12 contain 
curves showing the variations produced by the various conditions. 
EXCESSIVE HEAT 
The means of the spores in the control experiment were 32.40 ± 0.19 
X 19*79 ± o*o6 At. The means of the urediniospores cultured in high 
temperature (average for the generation being 81.8° F. with a maximum 
daily mean of 92.3° and minimum of 76.4°) were 29.25 ± 0.20 X 19.71 
± o.io At. An examination of Table XII shows that the difference in 
the means of the spore length in the control and temperature experi¬ 
ments was 11.25 times greater than its probable error, whereas the 
difference in the means of the width was exceeded by its probable error 
by 1.5 times; a significant 
difference for length, but none 
whatever for width. 
deficient eight 
In this experiment the 
urediniospores were cultured 
in a light intensity of a total 
average of 3.1 per cent with 
a maximum daily limit of 10 
per cent and a minimum of 
2 per cent. The light in¬ 
tensity readings were made 
three times a day with the aid 
of a Clements photometer. 
The means of the uredinio¬ 
spores in this test were 28.92 
±0.21 X 19.89 ±0.08 At, which 
were practically identical with 
those which prevailed in the 
case of excessive heat. Here, too, the difference was significant with re¬ 
spect to spore length only. The difference in the means of the width be¬ 
tween the control and shade was exactly the same as its probable error. 
Fig. II.—Differences in lengths of urediniospores of Puccinia 
graminis Iritici cultured imder favorable and adverse envi¬ 
ronmental conditions. 
DROUGHT 
The rusted plants in this test received a total amount of 100 cc. of 
water from the time they were removed from the incubation chamber 
until the time when the spore measurements were made, 14 days later. 
The water content of the soil at this time was determined on the basis 
of the ‘‘oven-dried” method and measured 5.38 per cent. The means 
of the urediniospores subjected to this condition were 30.51± 0.23 X 
19.31 ±0.07 Ai. Comparing these means with those of the control spores, 
we find a difference in both length and width which appears to be 
significant. 
A summary of the differences and their relations to the probable 
errors of the differences is given in Table XII. 
