Aug. is, 1914 
Head Smut of Sorghum and Maize 
35 i 
In summarizing the results for constructing these curves, the duration 
of presoaking in the modified treatments and the duration and tempera¬ 
ture of treatments have been approximated in several instances in order 
to bring all of them to intervals of 12 hours of presoaking, 5 minutes in 
duration of treatment, or 2 degrees in temperature. The results of 
treatments performed in 1909 and previously were recorded by counting 
heads, while subse¬ 
quently they were re¬ 
corded by noting the 
number of plants. 
These numbers are 
given at each point in 
the curves. 
It is evident from 
the curves in all these 
illustrations not only 
that the treatments in 
no way reduced the 
amount of infection, 
but also that, regard¬ 
less of treatment, the 
percentage of smutted 
plants occurring va¬ 
ried consistently with 
the season. Indeed, 
the curves in figures 
4, 5, and 6 proved to 
be, with scarcely an 
exception, 1 so nearly 
alike for all the treat¬ 
ments that they could 
not well be drawn to 
the same coordinates. 
They are therefore 
separated, and each 
curve is continued by 
a broken line to the axis of the coordinates to which it is drawn, each 
interval therefrom representing 1 per cent of infection. 
While it is true that infection by any phytopathogenic organism would 
vary with seasonal conditions regardless of the exact features of its life 
history, an added significance in these curves is found when it is noted that 
Fig. 5. —Curves summarizing fof different years the percentages of 
infection in plantings of Red Amber sorgo after modified hot-water 
treatments at all temperatures and of all presoakings, but after treat¬ 
ments of various durations. 
1 The only case in which these curves do not very nearly coincide is in the 54 0 C. treatments of 1909 (fig. 6). 
In this case there were but 151 heads on which to base the 1909 figure, this being so small that theresult, which 
is characteristic of the irregular occurrence of the infection at Amarillo, is plainly dependent upon some 
peculiar minor factor, such as a variation in soil conditions, rather than upon the season. It is certainly not 
owing to the treatment of the seed. 
