according to their weights, and those between certain weights put into cylinders, the cylinders, when arranged according to the size of the beans, will appear as shown in figure 72. An imaginary line running over the tops of the piles will give a curve (fig. 73) that corresponds to the curve of probability (fig. 74).
| Fig. 72. Beans put into cylindrical jars according to the sizes of the beans. The jars arranged according to size of contained beans. (After de Vries.) | Fig. 73. A curve resulting from arrangement of beans according to size. (After de Vries.) |
If we stand men in lines according to their height (fig. 75) we get a similar arrangement.
| Fig. 74. Curve of probability. | Fig. 75. Students arranged according to size. (After Blakeslee.) |
The differences in size shown by the individual beans or by the individual men are due in part to heredity, in part to the environment
in which they have developed. This is a familiar fact of almost every-day observation. It is well shown in the following example. In figure 76 the two boys and the two varieties of corn, which they are holding, differ in height. The pedigrees of the boys (fig. 77) make it probable that their height is largely inherited and the two races of corn are known to belong to a tall and a short race respectively. Here, then, the chief effect or difference is due to heredity. On the other hand, if individuals of the same race develop in a favorable environment the result is different from the development in an unfavorable environment, as shown in figure 78. Here to the right the corn is crowded and in consequence dwarfed, while to the left the same kind of corn has had more room to develop and is taller.
Fig. 76. A short and a tall boy each holding a stalk of corn—one stalk of a race of short corn, the other of tall corn. (After Blakeslee.)