Sit BULLETIN 754, U. S. DEPARTMENT OF AGRICULTURE. 
unchallenged as very good approximations of actual observation to © 
theory. 
The percentages of waxy seeds shown by the individual ears for 
the first-generation hybrids and those previously reported (7) have 
been plotted in figure 1, which shows that the deviation from 25 per 
cent is not the result of a few aberrant ears. It readily can be seen 
that while the mode and mean are considerably below the expected 
25 per cent, the curve very closely approximates the normal prob- 
ability curve. 
Although the graph (fig. 1) bears a striking resemblance to the 
normal probability curve, there is reason for believing that the indi- 
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Fic. 1.—Diagram showing the percentage of waxy seeds on 141 ears obtained from the 
second generation of the hybrids Dh 234 and Dh 237 and the ears previously reported. 
The dotted line shows the probability curve for this ponulawien of 141 ears, the mean 
and standard deviations being the same. 
viduals do not form a homogenous group deviating from a common 
mean. 
Asa means of determining whether the varying percentages of the 
individual ears are chance deviation from the mean of the entire 
group, a method has been proposed by ‘Yule (16) by which a theo- 
retical standard deviation is calculated, based on the harmonic mean 
of the observed individual ears. 
The “ goodness of fit” of the observed standard deviation to the 
calculated standard deviation is measured by the probable error of 
the former. 
