208 
Journal of Agricultural Research 
Vol. XXVI, No. 5 
Results 
Table V summarizes the results obtained in this experiment. From 
these data it will be seen that there was practically no difference between 
the amount of infection produced in the series held at 22 0 C. and that 
which was alternated between 14 0 and 30°. While there was a slight 
difference, it will be noted that the results of the seed inoculation series 
tend to neutralize those of the soil inoculation series; and in addition to 
this the variations are easily within the limits of experimental error. 
Table V .—Comparisons between the amounts of Helminthosporium infections on 
Harvest Queen wheat seedlings grown in soil held at constant temperatures of 14 0 , 22°, 
and 30° C. and those on similar seedlings grown in soil at temperatures alternating daily 
between 14 0 and 30° 
Seed inoculation. 
Soil inoculation. 
Soil temperature. 
Number of 
plants. 
Infection 
rating. 
Number of 
plants. 
Infection 
rating. 
# C. 
14 constant. 
108 
9.4 
109 
II -3 
22 constant. 
105 
19. 6 
104 
25- 1 
14 to 30 alternating. 
108 
20. 0 
109 
24. 2 
30 constant. 
86 
75-° 
84 
85.0 
While the results of this experiment show that plants grown at the 
mean temperature suffered practically the same degree of infection as 
those grown at the alternating temperatures, it should not be under¬ 
stood that this concept necessarily can be applied to all the possible 
combinations of time and temperature which might be arranged in ex¬ 
periments on this disease or on other diseases. The results of the constant 
temperature experiments cited herein show that time is an important 
factor in disease development; and, undoubtedly, prolonged periods of 
favorable temperatures do tend to produce more disease than short 
periods of such temperatures. IB 
Doubtless the relative position of the maximum and minimum tem¬ 
peratures selected on the disease curve established by the constant tem¬ 
perature experiment will influence results materially. It would seem 
probable that the results obtained in the alternating temperature experi¬ 
ment can hardly be expected to hold except when the maximum and 
minimum temperatures lie on the same side of the apex or optimum point 
of the disease curve established by constant temperature experiments. 
In view of the results of many physico-chemical experiments it does not 
seem reasonable to believe that the results above set forth would have 
been obtained if, for instance, the maximum and minimum temperatures 
had been selected in such a way as to include between them the apex or 
optimum of the constant-temperature disease curve. Further study is 
planned in connection with the various phases of the problems thus 
suggested. 
In his study on Fusarium blight, Dickson (4) reports that a short 
exposure to high temperatures during the germination period unbalanced 
the wheat seedling and thus made it susceptible to the parasite. The 
writer has not noted this relation in connection with the Helminthospo- 
