236 
Table 1 is a final summary of the data on the relation of temperature 
to development of the egg. For the present we are concerned only with 
columns 4 and 5—the reciprocals of the periods and the average mean 
daily temperatures. 
In preparing Graph 1, convenient fractional parts were laid off on 
the vertical axis corresponding to the reciprocals of the periods and divi- 
sions were made on the horizontal axis corresponding to the mean daily 
temperatures, and the one was plotted against the other. 
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Grapru 1. Incubation period. Reciprocals of the periods plotted 
against average mean daily temperatures. 
The points below 76 degrees fall approximately in a straight line, 
those above 76 are displaced to the right because for part of the time 
during the periods the temperature was above the degree of maximum 
rate of development. The reciprocal curve determined by the points 
below 76 degrees crosses the temperature axis at 49.32 degrees. Since 
it is probable that some of these points used are somewhat displaced, the 
upper ones somewhat to the right on account of temperatures higher than 
the degree of maximum rate of development, the lower ones to the left 
on account of temperatures below the zero of development, this line is 
probably a little too flat and the true line will cross the temperature axis 
above 49.32° rather than below it. Fifty degrees was taken as the 
approximate zero and was found to be nearly correct. 
The average daily day-degrees above 50 degrees were computed for 
the different groups, and the results are recorded in column 6 of Table 1. 
Next, the averages in column 6 were multiplied by the length of the 
