526 
STRUCTURE AND LIFE HISTORIES 
FIG. 394. Photograph of beans rolling down an inclined plane and 
accumulating at the base in compartments, which are closed in front by 
glass. The exposure was long enough to cause the moving beans to appear 
as caterpillar-like objects hopping along the board. If we assume that 
the irregularity of shape of the beans is such that each may make jumps 
either toward the right or toward the left in rolling down the board, the 
laws of chance lead us to expect that in very few cases will these jumps 
be all in the same direction, as indicated by the few beans collected in the 
compartments at the extreme right and left. Rather the beans will tend 
to jump in both right and left directions, the most probable condition 
being that in which the beans make an equal number of jumps to the right 
and to the left, as shown by the large number accumulated in the central 
compartment. If the board be tilted to one side, the curve of beans would 
be altered by this one-sided influence. In like fashion, a series of factors 
either of environment or of heredity if acting equally in both favorable 
and unfavorable directions, will cause a collection of ears of corn to assume 
a similar variability curve, when classified according to their relative size. 
Such curves, called Qutelet's curves, are used by biometricians in classify- 
ing and studying variations in plants and animals. (Photo by A. F. 
Blakeslee. Legend slightly modified from Journal of Heredity, June, 
1916.) 
